1. Expression
ISYS 350

2. Performing Calculations
Basic calculations such as arithmetic calculation can be performed by math operators
Operator
Name of the operator
Description +
Addition
Adds two numbers -
Subtraction
Subtracts one number from another *
Multiplication
Multiplies one number by another /
Division
Divides one number by another and gives the quotient %
Modulus
Divides 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);

3. Order of Evaluation Operator Multiples
1 ( ) Inner to outer, left to right
2. Power left to right
3. *, / left to right
4. +, - left to right

4. Formula to Expression

5. 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 = 7
int result8 = ++x; // result8 = 15, x = 15
++z; // z= 11
double a = 8.5;
double b = 3.4;
double result15 = --a; // result15 = 7.5
double result16 = ++b; // result16 = 4.4

6. Compound (Shortcut) Operators
+= 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.

8. 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)
//myInt += 1;
//myInt = ++myInt;
++myInt;
textBox1.Text = myInt.ToString(); }

9. 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)
myInt += stepValue;
// myInt = myInt + stepValue;

10. 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.

11. 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?

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

13. 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.