C Programming Day 2 - PowerPoint Presentation

Slide1

C Programming Day 2based upon Practical C Programming by Steve Oualline

CS550

Operating SystemsSlide2

Variable NamesVariable names must start with a letter or an underscoreNo special characters may be used in variable names

Letters, digits, or underscores may follow the first character in the variable nameSlide3

Variable Name ExamplesValid

avg

_pi

number_of_students

inT

Invalid

int

double

the end

3rd_entry

all$doneSlide4

Escape codes\n new line

\r

return

\t

tab

\' single quote\" double quote\\ backslashSlide5

Floating Point vs. Integer Division

19/10 --> 1

R

emember to truncate after the decimal point for integer division

19.0 / 10.0 --> 1.9

19.0 / 10 --> 1.919 / 10.0 --> 1.9Slide6

Character Data Typechar - denotes the character data type and holds one character

char a;Slide7

Example Code#include <

stdio.h

>

int

main(int argc, char **

argv

)

{

char c; //Declaration

c = 'A'; //Initialization

printf

("%c\n", c); //print contents of c

printf

("%d\n", c); //print c as an

int

printf

(”%u\n", &c); //print the address of c

//Assume the address is 1000

return 0;

}Slide8

OutputA

65

1000

Notice that the ASCII code for 'A' is output

ASCII codes can be found on the web

http://www.asciitable.com/Slide9

Reading Data with scanf

Pretend

a

has an address of 205

&a is 205 in C because the ampersand means “address of”int a;

printf

("Please enter an integer: ");

scanf

("%d", &a); //Read data into

//memory location 205

printf

("a is %d\n", a);

printf

("The address of a is %u\n", &a);Slide10

Running the programgcc

addrEx.c

–o

addrEx.exe

or with the Intel compilericc

addrEx.c

–o

addrEx.exe

Output:

Please enter an integer: 5

a is 5

The address of a is 205Slide11

Multiple inputs with scanf

int

a, b, c;

printf

("Enter 3

ints on one line: ");scanf

("%d %d %d", &a, &b, &c);

printf

("%d %d %d", a, b, c);

Enter 3

ints

on one line:

5 10 15

5 10 15Slide12

Field Width Specifiers

printf

("%c%4c%6c\n", ‘C', 'B', ‘A');

//Use 4 spaces for the 2nd character and 6 for the 3rd character

C___B_____A

printf

(”%2d", 3000);

3000

printf

("%5.2lf\n", 6.537);

__6.54Slide13

Common number of bytes used on 64-bit machineschar

--> 1 byte

float

--> 4 bytes

double

--> 8 byteslong double --> 16 bytesint --> 4 byteslong --> 8 bytes

Try the following:

printf

("%u\n",

sizeof

(char));

Note that

%u

represents an

unsigned

intSlide14

ArraysAn array is a sequence of data items that are of the same type and are stored contiguously in memory.

Elements of an array are accessed using square brackets [].

Arrays in C are indexed from zero.

type name[size]; //Array declaration

//note that the size cannot be changedSlide15

Exampleint

intarr

[1000];

0 1 2 999

+---+---+---+--------------------+---+| | | | . . . | |

+---+---+---+--------------------+---+

Attempting to access data beyond the end of an array will often, but not always, result in a segmentation fault. Slide16

Other Exampleschar

carr

[4];

double

darr

[27];unsigned char ucarr[78];

long

larr

[12];Slide17

More on ArraysAn array's size cannot be changed.

d

ouble

darr

[27];

We use a subscript or index to access an element of an array.darr[0]

darr

[19]Slide18

More on Arraysdarr is the name of the array and represents the address of the first element in the array

darr

== 200

index 0 1 2 26

+---+---+---+--------------------+---+ |2.3|5.4|0.2| . . . |7.3|

+---+---+---+--------------------+---+

200 208 216 408

addressSlide19

Addressing ArraysNotice the address changes by 8 because double values take up 8 bytes.

Example

darr

[20]

darr

+ index*sizeof(double)

darr

is the starting point in memory.

The rest is the offset from the starting point

Notice that

darr

is actually an unsigned integerSlide20

Another Exampleint

arr

[5] = {7, 25, 13, 2, -3};

0 1 2 3 4

+---+---+---+---+---+ | 7 | 25| 13| 2 |-13| +---+---+---+---+---+

We can also use the following and get the same effect

int

arr

[] = {7, 25, 13, 2, -3};Slide21

Yet Another Exampledouble data[5] = { 34.0, 27.0, 45.0, 82.0, 22.0 };

double total,

avg

;

total = data[0] + data[1] + data[2] + data[3] + data[4];

avg

= total / 5.0;

printf

("Total %lf\

nAvg

%lf\n", total,

avg

);Slide22

ASCII Art of the Previous Example 0 1 2 3 4

+-----+-----+-----+-----+-----+

d

ata | 34.0| 27.0| 45.0| 82.0| 22.0|

+-----+-----+-----+-----+-----+

+-----+t

otal |210.0|

+-----+

+-----+

a

vg

| 42.0|

+-----+

Total 210.0

Avg

42.0Slide23

StringsIn C, a string is a one-dimensional array of characters (type char

).

Strings always end with a special character -- the

NULL

character

The NULL character is all caps in CThe character '\0', the integer 0, and

NULL

all represent the same null value in C.Slide24

Exampleschar a = '\0'; //The null character

0 1 2 3

+-----+-----+-----+-----+

"

abc

" | 'a' | 'b' | 'c' | '\0'|

+-----+-----+-----+-----+

The length of this string is 3.

The size of this array is 4.

When declaring an array that will contain a string, be sure to leave

one extra character of space for the null character.Slide25

String Exampleschar name[100];

name[0] = 'H';

name[1] = 'e';

name[2] = 'l';

name[3] = 'l';

name[4] = 'o';name[5] = '\0';

printf

("%s\n", name);

char name[] = "Hello";

char name[] = {'H', 'e', 'l', 'l', 'o', '\0'};Slide26

scanfYou

can

use

scanf

to read in a string.

char name[100];printf("Enter your name: ");scanf("%s", name); //Recall that name is the

//address of the beginning

//of the array (string).Slide27

scanf

Enter your name: Dave

0 1 2 3 4

+-----+-----+-----+-----+-----+---------name | 'D' | 'a' | 'v' | 'e' | '\0'| . . .

+-----+-----+-----+-----+-----+---------Slide28

Math Functions in C#include <

math.h

> //to use math functions

x^y

is

pow(x,y)pow(2,2) --> 2^2 = 4double d;d =

pow

(2,3);

d now contains 8.0Slide29

Math Functions in C A few other math functions:

cos

(x)

tan(x)

sin(x) sqrt(x)

d =

sqrt

(50 + 50);

//d will contain 10.0Slide30

Example

#include <

stdio.h

>

#include <

math.h>int

main() {

double

a,b,c

;

a = 3; b = 4;

//compute the square root of a^2 + b^2

c =

sqrt

(

pow

(a,2) +

pow

(b,2));

printf

("%lf is a, %lf is b, and %lf is c\n", a, b, c);

printf

("%lf is a, %lf is b, and %lf is c\n", a, b,

sqrt

(a*a + b*b) );

return 0;

}Slide31

Problems with strings and scanf

char line[100];

scanf

("%s", line); //line is the address

printf

("%s\n", line);Assume an input of:Hello there

The output will be:

Hello

Why?

scanf

counts white space as a delimiter.Slide32

fgets

fgets

reads an entire line. Similar to

Scanner.readLine

()

Be sure to leave lots of space in your arrays when using fgets.Function call:fgets(

name of string

,

size of string in bytes

,

where the input is coming

from

);Slide33

Example of fgets

char name[50];

printf

("Please enter your name: ");

fgets

(name, sizeof(name),

stdin

);

//

sizeof

(name) returns the number

// of bytes in the array name.

//

stdin

is standard input. That

// means we read from the consoleSlide34

ResultPlease enter your name:

Dave

Monismith

Dave

Monismith

<-- has 14 charactersname 0 1 2 3 4 12 13 14 15

+-----+-----+-----+-----+-----+------+-----+-----+-----+-----+--------

| 'D' | 'a' | 'v' | 'e' | ' ' | . . .| 't' | 'h' | '\n'| '\0'| . . .

+-----+-----+-----+-----+-----+------+-----+-----+-----+-----+--------

Notice that the

'\n'

character is stored within our string.

We need to remove it.Slide35

String FunctionsUse

#include <

string.h

>

strlen

(name of string)Provides the length of the string and excludes null character.

strlen

(name)

is 15

We can remove the return character from

name

as follows:

name[

strlen

(name) - 1] = 0;Slide36

sscanf

sscanf

is string

scanf

sscanf(name of string, control string, variables);Slide37

Example

#include <

stdio.h

>

#include <

string.h>int main(

int

argc

, char **

argv

){

int

a, b;

char line[100];

fgets

(

line,sizeof

(line),

stdin

);

sscanf

(line, "%d %d", &a, &b);

printf

("%d %d\n", a, b);

}Slide38

String FunctionsTo use string functions,

#include <

string.h

>

Sometimes compilers will let you get away without it.

strlen - # of characters in a stringstrcpy - allows you to copy the contents of one string into another

strcpy

(destination, source);

strcat

- allows you to concatenate (add to) a string to the end of another string

strcat

(destination, source);

Do NOT use the + operator as you would in Java

name1 = name1 + name2; //Don't do this in CSlide39

Example

char first[100];

char last[100];

char

full_name

[200];printf("%s%s

","Please enter your ",

"first name: ");

fgets

(first,

sizeof

(first),

stdin

);

fgets

(last,

sizeof

(last),

stdin

);Slide40

Example//Remove newline characters

first[

strlen

(first) - 1] = '\0';

last[

strlen(first) - 1] = '\0';strcpy

(

full_name

, first);

strcat

(

full_name

, " ");

strcat

(

full_name

, last);

printf

("%s\n",

full_name

);Slide41

String Comparison

strcmp

(str1, str2)

result is zero if two strings are lexicographically equivalent

A

--> 65a --> 97Try the following:

strcmp

("a", "a");

strcmp

("A", "a");

strcmp

("a", "A");Slide42

Shorthand Operatorsa = a + 2;

is the same as

a += 2

Other operators include

+= -= *= /=Slide43

Pre/Post Operators++ adds one to a variable/expression (increment)-- subtracts one from a variable or expression (decrement)

a++; //Post increment

++a; //Pre incrementSlide44

Pre Increment Example//Try this

a = 1;

printf

("%d\n", ++a);

//Result is the same as

a = a + 1;printf

("%d\n", a);Slide45

Post Increment Example//Try this

a = 1;

printf

("%d\n", a++);

//Result is the same as

printf("%d\n", a);

a = a +1;Slide46

Problems with Pre/Post Incrementvalue = 1;

//Results from the following assignment

//statement are undefined in the

//C standard

result = (value++ * 5) + (value++ * 3);Slide47

Example Answer 1Evaluation could occur as follows:

1 * 5 = 5

value = 2

2 * 3 = 6

value = 3

result = 11Slide48

Example Answer 2Or:

1 * 3 = 3

value

= 2

2 * 5 = 10

value

= 3

result

= 13Slide49

Assignment OperatorDon't play around with the assignment operator either

a = (b = 2) + (c = 3);

//is a valid C statement

//Don't do this!Slide50

Multi-dimensional Arrays

type

arrayname

[dim1][dim2][dim3]...

int

arr[2][3]; Example

arr

[1][0] = 23;