3 : Decisions

The if statement is used to implement a decision.

The if statement has two parts: a test and a body.

The body of the if consists of statements.

            if (condition)

            {

                 statement1;

                 statement2;

                 .  .   .

            }

Decisions

To implement alternative conditions, use the if/else statement.

            if (condition)

            {

                statement;

                .  .  .

            }

            else

                statement;

                .  .  .

            }

Decisions

            if (condition)
                        statement;
            else if (condition)
                        statement;
            else if (condition)
                        statement;
            else
                        statement;

Relational Operators

Equality:        = =  (Equal)
                        ! =  (Not Equal)
Relational:         >  
                        >= 
                        <  
                        <= 
Logical:            &&  (AND)
                        | |   (OR)
                        !     (NOT)

Example
int x = 10, y = 20;
if (x = = 10 && y > = 15) {….}

public class Compare {
   public static void main(String[] args) {
                int num1 = Integer.parseInt(args[0]);
                int num2 = Integer.parseInt(args[1]);
                if (num1 > num2)
                   System.out.println(num1+“is greater than” +num2);
                else if (num2 > num1)
                   System.out.println(num2 + “ is greater than ” + num1);
                else
                   System.out.println(num2 + “ is equal to ” + num1);
     }
 }

 - Complie c:> javac Compare.java
 - Run     c:> java Compare 10 20

Selection Operator

            condition ? expression1 : expression2
if (a > b)
                        z = a;
            else
                        z = b;
==>     z = (a > b) ? a : b;

switch statement

                switch (expression) {
                   case value1 : statements;
                                                                break;
                   case value2 : statements;
                                                                break;
                   case …
                   default:               statements;
                }

Remember!

The test cases of the switch statement must be constant, and they must be integers.

You can not use a switch to branch on floating-point or string values.

Every branch of the switch is terminated by a break instruction.

For Example :

int num;
...
switch (num) {
   case 1 : System.out.print(“one”); break;
   case 2 : System.out.print(“two”); break;
   case 3 : System.out.print(“three”); break;
   case 4 : System.out.print(“four”); break;
   case 5 : System.out.print(“five”); break;
   default: System.out.println(“Invalid number”);
}
…

Iteration

while statement

                while (expression) {
                                statement;
                }

Example:

                i = 1;
                while (i <= 5) {
                                System.out.println(“Hello ”  + i);
                                i++;
                }

do-while statement

                do {
                   statement
                } while (expression)

Example:

                i = 1;
                do {
                   System.out.println(“Hello ” + i);
                   i++;
                } while (i > 5);

for statement

   for (expression1; expression2; expression3)
                statement;

Example:

   for (i = 1; i <= 5; i++)
                System.out.println(“Hello ”          + i);

The  break  and  continue  statements

The break statement can be used to exit a while, for, or do loop.

                i = 1;
                while (i <= 10) {
                    System.out.println(“Hello ” + i);
                    if (i = = 6)
                                break;
                    i++;
                }

The continue statement is another goto-like statement.
It jumps to the end of the  current iteration of the loop.

i = 1;
                while (i <= 10) {
                    System.out.println(“Hello ” + i);
                    if (i = = 6) {
                                 i++;
                                 continue; // jump to the end of the loop body

i++;
                }

Exercise

   Write a program to read the rank order and five integers then determine, and print the largest and smallest integers in the format shown below.. Do not use pre-defined Math methods.

Number inputs: 27, 83, 15, 94, 25 
The smallest number is 15
The largest number is 94