Debasis Samanta Computer Science & Engineering
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Debasis Samanta Computer Science Engineering Indian Institute of Technology Kharagpur Spring-2017 Programming and Data Structures Lecture 4 Arrays and Strings Lecture 04: DSamanta CS 11001 : Programming and Data Structures Arrays
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01
Debasis Samanta
Computer Science & Engineering
Indian Institute of Technology Kharagpur
Spring-2017 Programming and Data Structures<br>
Computer Science & Engineering
Indian Institute of Technology Kharagpur
Spring-2017 Programming and Data Structures<br>
02
Lecture #4
Arrays and Strings Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
Arrays and Strings Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
03
Arrays
Basic concept
1-Dimensional Arrays
Declaration of 1-D arrays in C programs
Initialization of 1-D arrays
Some C programs dealing with 1-D arrays
2-Dimensional Arrays
Declaration of 2-D arrays in C programs
Initialization of 2-D arrays
Some C programs dealing with 1-D arrays Today’s Discussion… Lecture #04: © DSamanta CS 11001 : Programming and Data Structures Strings
Basic concepts
Declaration of strings in C
Initialization of a string
C-library functions for strings
Some C-programs with strings<br>
Basic concept
1-Dimensional Arrays
Declaration of 1-D arrays in C programs
Initialization of 1-D arrays
Some C programs dealing with 1-D arrays
2-Dimensional Arrays
Declaration of 2-D arrays in C programs
Initialization of 2-D arrays
Some C programs dealing with 1-D arrays Today’s Discussion… Lecture #04: © DSamanta CS 11001 : Programming and Data Structures Strings
Basic concepts
Declaration of strings in C
Initialization of a string
C-library functions for strings
Some C-programs with strings<br>
04
Arrays Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
05
Some Examples of Arrays Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
06
Basic Concept Many applications require multiple data items that have common characteristics.
In mathematics, we often express such groups of data items in indexed form
x1, x2, x3, …, xn
Why are arrays essential for some applications?
Reading some numbers from the keyboard and then
Sort them in ascending order.
To find the mode and standard deviation.
etc.
How such a set of data can be stored in computer and subsequently process them? Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
In mathematics, we often express such groups of data items in indexed form
x1, x2, x3, …, xn
Why are arrays essential for some applications?
Reading some numbers from the keyboard and then
Sort them in ascending order.
To find the mode and standard deviation.
etc.
How such a set of data can be stored in computer and subsequently process them? Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
07
Basic Concept Lecture #04: © DSamanta CS 11001 : Programming and Data Structures 1-D array 2-D array 3-D array<br>
08
1-D Arrays Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
09
Arrays Homogenous data types
All the data items constituting the group share the same name.
int x[10];
Individual elements are accessed by specifying the index. Lecture #04: © DSamanta x is a 10-element one dimensional array x[0] x[1] x[2] x[9] CS 11001 : Programming and Data Structures<br>
All the data items constituting the group share the same name.
int x[10];
Individual elements are accessed by specifying the index. Lecture #04: © DSamanta x is a 10-element one dimensional array x[0] x[1] x[2] x[9] CS 11001 : Programming and Data Structures<br>
10
Declaring Arrays Like variables, the arrays that are used in a program must be declared before they are used.
General syntax:
type array-name [size];
type specifies the type of element that will be contained in the array (int, float, char, etc.)
size is an integer constant which indicates the maximum number of elements that can be stored inside the array.
Example
int marks[5];
Here, marks is an array containing a maximum of 5 integers. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
General syntax:
type array-name [size];
type specifies the type of element that will be contained in the array (int, float, char, etc.)
size is an integer constant which indicates the maximum number of elements that can be stored inside the array.
Example
int marks[5];
Here, marks is an array containing a maximum of 5 integers. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
11
Examples Examples:
int x[10];
char line[80];
float points[150];
char name[35];
Be careful!
If we are not sure of the exact size of the array, we can define an array of a large size.
int marks[50];
there is no element like x[50], x[-1], x[100], etc.
The following kind of usage is illegal:
int n;
int marks[n]; Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
int x[10];
char line[80];
float points[150];
char name[35];
Be careful!
If we are not sure of the exact size of the array, we can define an array of a large size.
int marks[50];
there is no element like x[50], x[-1], x[100], etc.
The following kind of usage is illegal:
int n;
int marks[n]; Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
12
How an array is stored in memory? Starting from a given memory location, the successive array elements are allocated space in consecutive memory locations.
Here,
x is the starting address of the array in memory
The array index starts at zero. That is, the location of a[0] is at x
Let k is the number of bytes allocated per array element
Element a[i] is allocated at the memory location having address x + i*k Lecture #04: © DSamanta x x+k x+2k a CS 11001 : Programming and Data Structures<br>
Here,
x is the starting address of the array in memory
The array index starts at zero. That is, the location of a[0] is at x
Let k is the number of bytes allocated per array element
Element a[i] is allocated at the memory location having address x + i*k Lecture #04: © DSamanta x x+k x+2k a CS 11001 : Programming and Data Structures<br>
13
A Warning In C, while accessing array elements, array bounds are not checked.
Example:
int marks[5];
:
:
marks[8] = 75;
The above assignment would not report any error; however, execution will fail.
Rather, it may result in unpredictable program results. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
Example:
int marks[5];
:
:
marks[8] = 75;
The above assignment would not report any error; however, execution will fail.
Rather, it may result in unpredictable program results. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
14
Initialization of Arrays General form
type array_name[size] = { list of values };
Examples
int marks[5] = {72, 83, 65, 80, 76};
char name[4] = {‘A’, ‘m’, ‘i’, ‘t’};
Some special cases
If the number of values in the list is less than the number of elements, then the remaining elements are automatically set to zero.
float total[5] = {24.2, -12.5, 35.1};
total[0]=24.2, total[1]=-12.5, total[2]=35.1,
total[3]=0, total[4]=0 Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
type array_name[size] = { list of values };
Examples
int marks[5] = {72, 83, 65, 80, 76};
char name[4] = {‘A’, ‘m’, ‘i’, ‘t’};
Some special cases
If the number of values in the list is less than the number of elements, then the remaining elements are automatically set to zero.
float total[5] = {24.2, -12.5, 35.1};
total[0]=24.2, total[1]=-12.5, total[2]=35.1,
total[3]=0, total[4]=0 Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
15
Initialization of Arrays If the size declares is less than the elements in the initialization, then the excess elements will be ignored
float total[5] = {2.2, -1.5, 3.5, 0.1, 0.2, 0.4};
The last element namely 0.4 will be ignored!
The size may be omitted. In such cases the compiler automatically allocates enough space for all initialized elements.
int flag[] = {1, 1, 1, 0};
char name[] = {‘A’, ‘m’, ‘i’, ‘t’}; Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
float total[5] = {2.2, -1.5, 3.5, 0.1, 0.2, 0.4};
The last element namely 0.4 will be ignored!
The size may be omitted. In such cases the compiler automatically allocates enough space for all initialized elements.
int flag[] = {1, 1, 1, 0};
char name[] = {‘A’, ‘m’, ‘i’, ‘t’}; Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
16
Example 1: Find the minimum of a Set of 10 Numbers Lecture #04: © DSamanta #include <stdio.h>
main()
{
int a[10], i, min;
for (i=0; i<10; i++)
scanf (“%d”, &a[i]);
min = 99999;
for (i=0; i<10; i++)
{
if (a[i] < min)
min = a[i];
}
printf (“\n Minimum is %d”, min);
} Array declaration Reading array element Assessing array element CS 11001 : Programming and Data Structures<br>
main()
{
int a[10], i, min;
for (i=0; i<10; i++)
scanf (“%d”, &a[i]);
min = 99999;
for (i=0; i<10; i++)
{
if (a[i] < min)
min = a[i];
}
printf (“\n Minimum is %d”, min);
} Array declaration Reading array element Assessing array element CS 11001 : Programming and Data Structures<br>
17
Alternate Version #1 Lecture #04: © DSamanta #include <stdio.h>
#define size 10
main()
{
int a[size], i, min;
for (i=0; i<size; i++)
scanf (“%d”, &a[i]);
min = 99999;
for (i=0; i<size; i++)
{
if (a[i] < min)
min = a[i];
}
printf (“\n Minimum is %d”, min);
} Change only one line to change the problem size. CS 11001 : Programming and Data Structures<br>
#define size 10
main()
{
int a[size], i, min;
for (i=0; i<size; i++)
scanf (“%d”, &a[i]);
min = 99999;
for (i=0; i<size; i++)
{
if (a[i] < min)
min = a[i];
}
printf (“\n Minimum is %d”, min);
} Change only one line to change the problem size. CS 11001 : Programming and Data Structures<br>
18
Alternate Version #2 Lecture #04: © DSamanta #include <stdio.h>
main()
{
int a[100], i, min, n;
scanf (“%d”, &n); /* Number of elements */
for (i=0; i<n; i++)
scanf (“%d”, &a[i]);
min = 99999;
for (i=0; i<n; i++)
{
if (a[i] < min)
min = a[i];
}
printf (“\n Minimum is %d”, min);
} Define an array of large size and use only the required number of elements. CS 11001 : Programming and Data Structures<br>
main()
{
int a[100], i, min, n;
scanf (“%d”, &n); /* Number of elements */
for (i=0; i<n; i++)
scanf (“%d”, &a[i]);
min = 99999;
for (i=0; i<n; i++)
{
if (a[i] < min)
min = a[i];
}
printf (“\n Minimum is %d”, min);
} Define an array of large size and use only the required number of elements. CS 11001 : Programming and Data Structures<br>
19
Example 2: Computing GPA Lecture #04: © DSamanta #include <stdio.h>
#define nsub 6
main()
{
int grade_pt[nsub], cred[nsub], i,
gp_sum=0, cred_sum=0, gpa;
for (i=0; i<nsub; i++)
scanf (“%d %d”, &grade_pt[i], &cred[i]);
for (i=0; i<nsub; i++)
{
gp_sum += grade_pt[i] * cred[i];
cred_sum += cred[i];
}
gpa = gp_sum / cred_sum;
printf (“\n Grade point average: is %d”, gpa);
} Handling two arrays at the same time. CS 11001 : Programming and Data Structures<br>
#define nsub 6
main()
{
int grade_pt[nsub], cred[nsub], i,
gp_sum=0, cred_sum=0, gpa;
for (i=0; i<nsub; i++)
scanf (“%d %d”, &grade_pt[i], &cred[i]);
for (i=0; i<nsub; i++)
{
gp_sum += grade_pt[i] * cred[i];
cred_sum += cred[i];
}
gpa = gp_sum / cred_sum;
printf (“\n Grade point average: is %d”, gpa);
} Handling two arrays at the same time. CS 11001 : Programming and Data Structures<br>
20
Things You Cannot Do You cannot
Suppose, a and b are two array names.
They cannot be used as ordinary variables
use = to assign one array variable to another is not possible
a = b; /* a and b are arrays */
use == to directly compare array variables is not allowed
if (a == b) ………
directly scanf or printf arrays is not possible
printf (“……”, a); Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
Suppose, a and b are two array names.
They cannot be used as ordinary variables
use = to assign one array variable to another is not possible
a = b; /* a and b are arrays */
use == to directly compare array variables is not allowed
if (a == b) ………
directly scanf or printf arrays is not possible
printf (“……”, a); Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
21
Accessing Array int a[25], b[25];
How to copy the elements of one array to another?
By copying individual elements
for (j=0; j<25; j++)
a[j] = b[j];
By reading them one element at a time
for (j=0; j<25; j++)
scanf (“%f”, &a[j]);
The ampersand (&) is necessary. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures Note:
The elements can be entered all in one line or in different lines.<br>
How to copy the elements of one array to another?
By copying individual elements
for (j=0; j<25; j++)
a[j] = b[j];
By reading them one element at a time
for (j=0; j<25; j++)
scanf (“%f”, &a[j]);
The ampersand (&) is necessary. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures Note:
The elements can be entered all in one line or in different lines.<br>
22
Accessing Array int a[25];
Printing Array (array elements)
By printing them one element at a time.
for (j=0; j<25; j++)
printf (“\n %f”, a[j]);
The elements are printed all in one line (starting with a new line).
printf (“\n”);
for (j=0; j<25; j++)
printf (“%f”, a[j]); Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
Printing Array (array elements)
By printing them one element at a time.
for (j=0; j<25; j++)
printf (“\n %f”, a[j]);
The elements are printed all in one line (starting with a new line).
printf (“\n”);
for (j=0; j<25; j++)
printf (“%f”, a[j]); Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
23
2-D Arrays Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
24
Two Dimensional Arrays Many applications require us to store a table of values.
The table contains a total of 20 values, five in each line.
The table can be regarded as a matrix consisting of four rows and five columns.
C allows us to define such tables of items by using 2-D arrays. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
The table contains a total of 20 values, five in each line.
The table can be regarded as a matrix consisting of four rows and five columns.
C allows us to define such tables of items by using 2-D arrays. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
25
Declaring 2-D Arrays General form:-
type array_name [row_size][column_size];
Examples
int marks[4][5];
float sales[12][25];
double matrix[100][100]; Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
type array_name [row_size][column_size];
Examples
int marks[4][5];
float sales[12][25];
double matrix[100][100]; Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
26
Accessing Elements of a 2-D Array Similar to that for 1-D array, but use two indices.
Examples
x[m][n] = 0;
c[i][k] += a[i][j] * b[j][k];
First indicates row, second indicates column.
Both the indices may be expressions which would evaluate to integer values.
x = sqrt (a[j*3][k+2]); Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
Examples
x[m][n] = 0;
c[i][k] += a[i][j] * b[j][k];
First indicates row, second indicates column.
Both the indices may be expressions which would evaluate to integer values.
x = sqrt (a[j*3][k+2]); Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
27
Storing a 2-D Array in Memory Starting from a given memory location, the elements are stored row-wise in consecutive memory locations.
x: starting address of the array in memory
c: number of columns
k: number of bytes allocated per array element
a[i][j] :: is allocated memory location at
address x + (i * c + j) * k Lecture #04: © DSamanta a[0]0] a[0][1] a[0]2] a[0][3] a[1][0] a[1][1] a[1][2] a[1][3] a[2][0] a[2][1] a[2][2] a[2][3] Row 0 Row 1 Row 2 CS 11001 : Programming and Data Structures<br>
x: starting address of the array in memory
c: number of columns
k: number of bytes allocated per array element
a[i][j] :: is allocated memory location at
address x + (i * c + j) * k Lecture #04: © DSamanta a[0]0] a[0][1] a[0]2] a[0][3] a[1][0] a[1][1] a[1][2] a[1][3] a[2][0] a[2][1] a[2][2] a[2][3] Row 0 Row 1 Row 2 CS 11001 : Programming and Data Structures<br>
28
Reading the Elements of a 2-D Array By reading them one element at a time.
for (i=0; i < nrow; i++)
for (j=0; j < ncol; j++)
scanf (“%f”, &a[i][j]);
The ampersand (&) is necessary.
Note:
The elements can be entered all in one line or in different lines. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
for (i=0; i < nrow; i++)
for (j=0; j < ncol; j++)
scanf (“%f”, &a[i][j]);
The ampersand (&) is necessary.
Note:
The elements can be entered all in one line or in different lines. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
29
Printing the Elements of a 2-D Array By printing them one element at a time.
for (i=0; i<nrow; i++)
for (j=0; j<ncol; j++)
printf (“\n %f”, a[i][j]);
The elements are printed one per line.
for (i=0; i<nrow; i++)
for (j=0; j<ncol; j++)
printf (“%f”, a[i][j]); Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
for (i=0; i<nrow; i++)
for (j=0; j<ncol; j++)
printf (“\n %f”, a[i][j]);
The elements are printed one per line.
for (i=0; i<nrow; i++)
for (j=0; j<ncol; j++)
printf (“%f”, a[i][j]); Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
30
Printing the Elements of a 2-D Array The elements are printed nicely in matrix form.
for (i=0; i<nrow; i++)
{
printf (“\n”);
for (j=0; j<ncol; j++)
printf (“%f ”, a[i][j]);
} Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
for (i=0; i<nrow; i++)
{
printf (“\n”);
for (j=0; j<ncol; j++)
printf (“%f ”, a[i][j]);
} Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
31
Example 1: Reading a Matrix Amxn Read the element of a matrix of integers of size mxn Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
32
Example 2: Matrix Addition Find the sum of two matrix amxn and bmxn anddtore the result in cmxn Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
33
Example 3: Matrix Multiplication Find the product of two matrices amxp and bpxn and store the result in cmxn Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
34
Arrays Beyond 2-D C language allows arrays of three or more dimensions. The general form of a multi-dimensional array is
type array_name[s1][s2][s3]…[sn];
Here, si is the size of the i-th dimension.
Examples.
int rainFall [day][month][city];
will store the rainfall data for each day in a year and for a number of cities.
float table[2][3][4] = {{{1.0, 2.0, 3.0}, {4.0, 5.0, 6.0}},……};
declares a 3-D array table with 24 float values and initialize the first and second rows of the first entries in the third dimension. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
type array_name[s1][s2][s3]…[sn];
Here, si is the size of the i-th dimension.
Examples.
int rainFall [day][month][city];
will store the rainfall data for each day in a year and for a number of cities.
float table[2][3][4] = {{{1.0, 2.0, 3.0}, {4.0, 5.0, 6.0}},……};
declares a 3-D array table with 24 float values and initialize the first and second rows of the first entries in the third dimension. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
35
Strings Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
36
Introduction A string is an array of characters.
Individual characters are stored in memory in ASCII code.
A string is represented as a sequence of characters terminated by the null (‘\0’) character. Lecture #04: © DSamanta “Hello” CS 11001 : Programming and Data Structures<br>
Individual characters are stored in memory in ASCII code.
A string is represented as a sequence of characters terminated by the null (‘\0’) character. Lecture #04: © DSamanta “Hello” CS 11001 : Programming and Data Structures<br>
37
Character Arrays and Strings char C[8] = {‘d',‘e',‘b',‘a',‘s',‘i',‘s','\0'};
C[0] gets the value ‘d', C[1] the value ‘e', and so on. The last (7th) location receives the null character ‘\0’.
Null-terminated character arrays are also called strings.
Strings can be initialized in an alternative way. The last declaration is equivalent to
char C[16] = “India is great!";
The trailing null character is missing here. C automatically puts it at the end.
Note also that for individual characters, C uses single quotes, whereas for strings, it uses double quotes. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
C[0] gets the value ‘d', C[1] the value ‘e', and so on. The last (7th) location receives the null character ‘\0’.
Null-terminated character arrays are also called strings.
Strings can be initialized in an alternative way. The last declaration is equivalent to
char C[16] = “India is great!";
The trailing null character is missing here. C automatically puts it at the end.
Note also that for individual characters, C uses single quotes, whereas for strings, it uses double quotes. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
38
Declaring String Variables A string is declared like any other array:
char string-name [size];
Here, size determines the number of characters in string_name (including for null character ‘\0’)
When a character string is assigned to a character array, it automatically appends the null character (‘\0’) at the end of the string. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures char C[16] = “India is great!";<br>
char string-name [size];
Here, size determines the number of characters in string_name (including for null character ‘\0’)
When a character string is assigned to a character array, it automatically appends the null character (‘\0’) at the end of the string. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures char C[16] = “India is great!";<br>
39
Examples char name[30];
char city[15];
char dob[11];
A string may be initialized at the time of declaration.
char city[15] = “Calcutta”;
char city[15] ={‘C’,‘a’,‘l’,’c’,‘u’,‘t’,’t’,‘a’};
char dob[] = “12-10-1975”; Lecture #04: © DSamanta Equivalent CS 11001 : Programming and Data Structures<br>
char city[15];
char dob[11];
A string may be initialized at the time of declaration.
char city[15] = “Calcutta”;
char city[15] ={‘C’,‘a’,‘l’,’c’,‘u’,‘t’,’t’,‘a’};
char dob[] = “12-10-1975”; Lecture #04: © DSamanta Equivalent CS 11001 : Programming and Data Structures<br>
40
Reading Strings from the Keyboard Two different cases will be considered
Reading words
Reading an entire line Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
Reading words
Reading an entire line Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
41
Reading “words” scanf can be used with the “%s” format specification.
char name[30];
:
:
scanf (“%s”, name);
The ampersand (&) is not required before the variable name with “%s”.
The problem here is that the string is taken to be upto the first white space (blank, tab, carriage return, etc.)
If we type “Debasis Samanta”
name will be assigned the string “Debasis”! Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
char name[30];
:
:
scanf (“%s”, name);
The ampersand (&) is not required before the variable name with “%s”.
The problem here is that the string is taken to be upto the first white space (blank, tab, carriage return, etc.)
If we type “Debasis Samanta”
name will be assigned the string “Debasis”! Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
42
Reading a “line of text” In many applications, we need to read in an entire line of text (including blank spaces).
We can use the getchar() function for the purpose. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
We can use the getchar() function for the purpose. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
43
Reading a “line of text” Lecture #04: © DSamanta char line[81], ch;
int c=0;
:
:
do
{
ch = getchar();
line[c] = ch;
c++;
}
while (ch != ‘\n’);
c = c – 1;
line[c] = ‘\0’; Read characters until CR (‘\n’) is encountered Make it a valid string CS 11001 : Programming and Data Structures<br>
int c=0;
:
:
do
{
ch = getchar();
line[c] = ch;
c++;
}
while (ch != ‘\n’);
c = c – 1;
line[c] = ‘\0’; Read characters until CR (‘\n’) is encountered Make it a valid string CS 11001 : Programming and Data Structures<br>
44
Reading a line :: Alternate Approach Lecture #04: © DSamanta char line[81];
:
:
scanf (“%[ABCDEFGHIJKLMNOPQRSTUVWXYZ]”, line); char line[81];
:
:
scanf (“%[^\n]”, line); Reads a string containing uppercase characters and blank spaces Reads a string containing any characters: CS 11001 : Programming and Data Structures<br>
:
:
scanf (“%[ABCDEFGHIJKLMNOPQRSTUVWXYZ]”, line); char line[81];
:
:
scanf (“%[^\n]”, line); Reads a string containing uppercase characters and blank spaces Reads a string containing any characters: CS 11001 : Programming and Data Structures<br>
45
Writing Strings to the Screen We can use printf with the “%s” format specification.
printf (“\n %s”, name);
Alternatively, we can use printf with the “%c” format and each character one after another.
i = 0;
while (name[i++] !=‘\0’)
printf(“%c”, name[i]); Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
printf (“\n %s”, name);
Alternatively, we can use printf with the “%c” format and each character one after another.
i = 0;
while (name[i++] !=‘\0’)
printf(“%c”, name[i]); Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
46
Processing Character Strings There exists a set of C library functions for character string manipulation.
strcpy :: string copy
strlen :: string length
strcmp :: string comparison
strtcat :: string concatenation
It is required to add the line.
#include <string.h> Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
strcpy :: string copy
strlen :: string length
strcmp :: string comparison
strtcat :: string concatenation
It is required to add the line.
#include <string.h> Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
47
strcpy() Works very much like a string assignment operator.
strcpy (string1, string2);
Assigns the contents of string2 to string1.
Examples:
strcpy (city, “Calcutta”);
strcpy (city, mycity);
Warning:
Assignment operator do not work for strings.
city = “Calcutta”; -> INVALID Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
strcpy (string1, string2);
Assigns the contents of string2 to string1.
Examples:
strcpy (city, “Calcutta”);
strcpy (city, mycity);
Warning:
Assignment operator do not work for strings.
city = “Calcutta”; -> INVALID Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
48
strlen() Counts and returns the number of characters in a string.
len = strlen (string);/* Returns an int */
The null character (‘\0’) at the end is not counted.
Counting ends at the first null character. Lecture #04: © DSamanta char city[15];
int n;
:
:
strcpy (city, “Calcutta”);
n = strlen (city); n is assigned 8 CS 11001 : Programming and Data Structures<br>
len = strlen (string);/* Returns an int */
The null character (‘\0’) at the end is not counted.
Counting ends at the first null character. Lecture #04: © DSamanta char city[15];
int n;
:
:
strcpy (city, “Calcutta”);
n = strlen (city); n is assigned 8 CS 11001 : Programming and Data Structures<br>
49
strcmp() Compares two character strings.
int strcmp (string1, string2);
Compares the two strings and returns 0 if they are identical; non-zero otherwise.
Examples:-
if (strcmp (city, “Delhi”) = = 0)
{ …… }
if (strcmp (city1, city2) ! = 0)
{ …… } Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
int strcmp (string1, string2);
Compares the two strings and returns 0 if they are identical; non-zero otherwise.
Examples:-
if (strcmp (city, “Delhi”) = = 0)
{ …… }
if (strcmp (city1, city2) ! = 0)
{ …… } Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
50
strcat() Joins or concatenates two strings together.
strcat (string1, string2);
string2 is appended to the end of string1.
The null character at the end of string1 is removed, and string2 is joined at that point.
Example:-
strcpy (name1, “Amit “);
strcpy (name2, “Roy“);
strcat (name1, name2); Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
strcat (string1, string2);
string2 is appended to the end of string1.
The null character at the end of string1 is removed, and string2 is joined at that point.
Example:-
strcpy (name1, “Amit “);
strcpy (name2, “Roy“);
strcat (name1, name2); Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
51
Example 2: Page Statistics Lecture #04: © DSamanta /* Read a line of text and count the number of uppercase in the text */
#include <stdio.h>
#include <string.h>
main()
{
char line[81];
int i, n, count=0;
scanf (“%[^\n]”, line);
n = strlen (line);
for (i=0; i<n; i++)
{
if (isupper (line[i])
count++;
}
printf (“\n The no. of uppercase ltr in the str %s is %d”,line, count);
} CS 11001 : Programming and Data Structures<br>
#include <stdio.h>
#include <string.h>
main()
{
char line[81];
int i, n, count=0;
scanf (“%[^\n]”, line);
n = strlen (line);
for (i=0; i<n; i++)
{
if (isupper (line[i])
count++;
}
printf (“\n The no. of uppercase ltr in the str %s is %d”,line, count);
} CS 11001 : Programming and Data Structures<br>
52
Example 1: Upper Case Counting Lecture #04: © DSamanta /* Read a text and count the number of uppercase letters */
#include <stdio.h>
#include <string.h>
#define MAX 1000;
main()
{
char myText[MAX];
int i, n, wCount=0; lCount = 0;
while ((c=getchar()) != 0) myText[i++] = c;
myText[i] = ‘\0’;
n = strlen (myText);
for (i=0; i<n; i++)
{
switch(myText[i]){
case ‘ ‘: wCount++; break;
case ‘\.’ :lcount++; break;
}
printf (“\n The number of words is %d and sentences is %d”,wCount, lCount);
} CS 11001 : Programming and Data Structures<br>
#include <stdio.h>
#include <string.h>
#define MAX 1000;
main()
{
char myText[MAX];
int i, n, wCount=0; lCount = 0;
while ((c=getchar()) != 0) myText[i++] = c;
myText[i] = ‘\0’;
n = strlen (myText);
for (i=0; i<n; i++)
{
switch(myText[i]){
case ‘ ‘: wCount++; break;
case ‘\.’ :lcount++; break;
}
printf (“\n The number of words is %d and sentences is %d”,wCount, lCount);
} CS 11001 : Programming and Data Structures<br>
53
Any question? You may post your question(s) at the “Discussion Forum” maintained in the course Web page. Lecture #04: © DSamanta CS 11001 : Programming and Data Structures<br>
54
Problems for Ponder… Lecture #04: © DSamanta An array of integer of size 10 is declared. Compiler then allocate memory for it
In which memory (cache, main memory, secondary memory) the memory is allocated?
If it is stored in maim memory, then in which part of the memory (data area, heap area or instruction area) it is stored?
How much memory (in Bytes), usually it will take?
Are they stored in contagious locations or distributed at random thorough the entire memory available?
Two arrays x and y are declared as follows.
float x[100] ; double y [100];
Which would take more amount? Why?
Suppose, you have declared an array long x[100]; Assume that the word size of the memory is 2 bytes. If the starting location of the array (i.e., the location of x[0]) in the memory is 1124, then what will be the memory location of x[8]? CS 11001 : Programming and Data Structures<br>
In which memory (cache, main memory, secondary memory) the memory is allocated?
If it is stored in maim memory, then in which part of the memory (data area, heap area or instruction area) it is stored?
How much memory (in Bytes), usually it will take?
Are they stored in contagious locations or distributed at random thorough the entire memory available?
Two arrays x and y are declared as follows.
float x[100] ; double y [100];
Which would take more amount? Why?
Suppose, you have declared an array long x[100]; Assume that the word size of the memory is 2 bytes. If the starting location of the array (i.e., the location of x[0]) in the memory is 1124, then what will be the memory location of x[8]? CS 11001 : Programming and Data Structures<br>
55
Problems for Ponder… Lecture #04: © DSamanta Suppose, we want to store the following data into an array, which is declared as char a2z [100];
11, 0, A, a, -1, 55, *
Is it possible to store them? If not, why?
What will be the memory location of a[i][j] in memory, if the starting location of the array is x and the 2-D array is stored in column major order? Assume, each element of the array needs w words of the memory.
What should be the memory locations in (a) row-major and (b) column major order of any non-zero elements of the following diagonal matrices. CS 11001 : Programming and Data Structures<br>
11, 0, A, a, -1, 55, *
Is it possible to store them? If not, why?
What will be the memory location of a[i][j] in memory, if the starting location of the array is x and the 2-D array is stored in column major order? Assume, each element of the array needs w words of the memory.
What should be the memory locations in (a) row-major and (b) column major order of any non-zero elements of the following diagonal matrices. CS 11001 : Programming and Data Structures<br>
56
Problems for Ponder… Lecture #04: © DSamanta Assume that array A and B are declared as follows:
int A[5][4];
int B[4];
Find the errors (if any), in the following program segments
for (i=1; i<4; i++)
scanf(“%f”, B[i]);
for (i=1; i<=5; i++)
for (j=1; i<=4; j++)
A[i][j] = 0;
for (i=4; i>=0; i--)
scanf(“%d”, &B[i]); CS 11001 : Programming and Data Structures<br>
int A[5][4];
int B[4];
Find the errors (if any), in the following program segments
for (i=1; i<4; i++)
scanf(“%f”, B[i]);
for (i=1; i<=5; i++)
for (j=1; i<=4; j++)
A[i][j] = 0;
for (i=4; i>=0; i--)
scanf(“%d”, &B[i]); CS 11001 : Programming and Data Structures<br>
57
Problems for Ponder… Lecture #04: © DSamanta String variables can be assigned values in the following four ways:
During type declaration
a) char name[] = “India”;
b) char name [ ] = {‘I’, ‘n’, ‘d’, ‘i’, ‘a’, ‘\0’};\
Using strcpy function
strcpy(aString, name);
Reading-in a string using scanf function
scanf(%s”, name);
Reading using gets function
gets(name);
What is the advantages and limitations in the above ways of initializing a string variable. Explain your answers with appropriate C programs.
It is required to store the name of 20 cities. Assume that name of a city should not exceed 20 characters. Give an idea how the data can be stored in a string matrix say myCities, tht is, myCity[i] will stored the name of the i-th city. CS 11001 : Programming and Data Structures<br>
During type declaration
a) char name[] = “India”;
b) char name [ ] = {‘I’, ‘n’, ‘d’, ‘i’, ‘a’, ‘\0’};\
Using strcpy function
strcpy(aString, name);
Reading-in a string using scanf function
scanf(%s”, name);
Reading using gets function
gets(name);
What is the advantages and limitations in the above ways of initializing a string variable. Explain your answers with appropriate C programs.
It is required to store the name of 20 cities. Assume that name of a city should not exceed 20 characters. Give an idea how the data can be stored in a string matrix say myCities, tht is, myCity[i] will stored the name of the i-th city. CS 11001 : Programming and Data Structures<br>
58
Problems for Practice… CS 10001 : Programming and Data Structures 58 Lecture #01: © DSamanta You can check the Moodle course management system for a set of problems for your own practice.
Login to the Moodle system at http://cse.iitkgp.ac.in/
Select “PDS Spring-2017 (Theory) in the link “My Courses”
Go to Topic 4: Practice Sheet #04 : Arrays and Strings
Solutions to the problems in Practice Sheet #04 will be uploaded in due time.<br>
Login to the Moodle system at http://cse.iitkgp.ac.in/
Select “PDS Spring-2017 (Theory) in the link “My Courses”
Go to Topic 4: Practice Sheet #04 : Arrays and Strings
Solutions to the problems in Practice Sheet #04 will be uploaded in due time.<br>
59
Lecture #01: © DSamanta CS 10001 : Programming and Data Structures 59 If you try to solve problems yourself, then you will learn many things automatically.
Spend few minutes and then enjoy the study.<br>
Spend few minutes and then enjoy the study.<br>