Expression - PowerPoint Presentation

Slide1

Expression

ISYS 350Slide2

Performing Calculations

Basic calculations such as arithmetic calculation can be performed by math operators

Operator

Name of the operator

Description+AdditionAdds two numbers-SubtractionSubtracts one number from another*MultiplicationMultiplies one number by another/DivisionDivides one number by another and gives the quotient%ModulusDivides one number by another and gives the remainder

Other calculations: Use Math class’s methods.

Example:

Math.Pow

(x, y)

double x = 3.0, y = 2.0, z;

z=

Math.Pow

(

x,y

);Slide3

Order of Evaluation

Operator Multiples

1 ( ) Inner to outer, left to right

2. Power left to right

3. *, / left to right4. +, - left to rightSlide4

Formula to ExpressionSlide5

Increment/Decrement Operators

++ Increment Adds 1 to the operand (x = x + 1).

--

Decrement Subtracts 1 from the operand (x = x - 1).

int x = 14;int y = 8;Int z = 10;int result7 = --y; // result7 = 7int result8 = ++x; // result8 = 15, x = 15++z; // z= 11double a = 8.5;double b = 3.4;double result15 = --a; // result15 = 7.5double result16 = ++b; // result16 = 4.4Slide6

Compound (Shortcut) Operators

Operator

+= Adding the operand to the starting value of the variable.

-=

Subtracting the operand from the starting value of the variable.*= Multiplying the operand by the starting value of the variable./= Dividing the operand by the starting value of the variable.%= Remainder after dividing the right operand by the value in the variable.Slide7
Slide8

Decrement/Increment by 1

private void button1_Click(object sender, EventArgs e)

{

int myInt;

myInt = int.Parse(textBox1.Text); // myInt-=1; // myInt = --myInt; --myInt; textBox1.Text = myInt.ToString(); } private void button2_Click(object sender, EventArgs e) { int myInt; myInt = int.Parse(textBox1.Text); //myInt += 1; //myInt = ++myInt; ++myInt; textBox1.Text = myInt.ToString(); }Slide9

Decrement/Increment by any Step Value

private void button1_Click(object sender,

EventArgs

e)

{ int stepValue; stepValue = int.Parse(textBox2.Text); int myInt; myInt = int.Parse(textBox1.Text); myInt -= stepValue; // myInt = myInt - stepValue; textBox1.Text = myInt.ToString(); } private void button2_Click(object sender, EventArgs e) { int stepValue; stepValue = int.Parse(textBox2.Text); int myInt; myInt = int.Parse(textBox1.Text); myInt += stepValue; // myInt = myInt + stepValue; textBox1.Text = myInt.ToString(); }Slide10

Prefix/Postfix Increment/Decrement Operators

int a = 5;

int b = 5;

int y = ++a; // a = 6, y = 6

int z = b++; // b = 6, z = 5•When you use an increment or decrement operator as a prefix to a variable, the variable is incremented or decremented and then the result is assigned. •When you use an increment or decrement operator as a postfix to a variable, the result is assigned and then the variable is incremented or decremented.Slide11

Counter

Example: Keep track the number of times a user clicks a button

Need to declare a variable:

int Counter=0;

Need to increase the counter by 1 when the button is clicked: Counter = Counter + 1; // Or Counter+=1; // Or ++Counter;Question: Where to declare this variable?Slide12

Example

int Counter = 0;

private void button1_Click(object sender, EventArgs e)

{

Counter = Counter + 1; textBox1.Text = Counter.ToString(); } private void button1_Click(object sender, EventArgs e) { int Counter = 0; Counter = Counter + 1; textBox1.Text = Counter.ToString(); }Incorrect:Correct:Slide13

Variable Scope

The scope of a variable determines its visibility to the rest of a program.

Procedural-level scope: declared in a procedure and visible only in the procedure.

Class-level scope: declared in a class but outside any procedure; visible to all procedures in the class.