Control statements 1.1 ( Decision making statements )

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Control statements

  • Control statements use to change the flow of program.

Decision making statements

  • We want one set of instructions to get executed in one situation, and an entirely different set in another situation. Such situations are dealt with in java program using a decision control or making instruction.
  • A decision control instruction can be implemented in java Using :
if-else statement
  • Java uses if-else to implement the decision control instruction.
Syntax:

if (this condition is true)
{
     execute statements1;
     execute statements2;
}
else
{
     execute statements3;
     execute statements4;
}
  • if statement : 
  1. if is a reserved keyword in java.
  2. if used to decide weather condition is satisfied or not.
  3. If a certain condition is true then if block will me execute otherwise not.
Syntax:

                if (this condition is true)
               {
                   execute statements1;
                   execute statements2;
                }

  • else if statement:
  1. combination of two keyword which is used to execute else condition of the program. 
else  + if  = else if  
Syntax:

              if (condition 1)
               {
                   execute statements1;
                   execute statements2;
                }
            else if (condition 2)
               {
                   execute statements3;
                   execute statements4;
                }

n conditions---------------------------continue
  • else statement : 
  1. else statement execute when every block of if and else if are false.
  2. There is no condition block only statements.

             if (condition 1)
               {
                   execute statements1;
                   execute statements2;
                }
            else if (condition 2)
               {
                   execute statements3;
                   execute statements4;
                }
           else
               {
                 execute statements5;
                 execute statements6;
               }

Flowchart:


Example:

Q1 .WAP to satisfy the condition ?

class program_1
{
   public static void main(String[] args)
  { 
       int a=10;
       if (a>20)
      {
        System.out.println("hello");
      } 
      else if(a<5)
     {
       System.out.println("hey");
      }
     else 
    {
      System.out.println("bye");
     }
    }
  }
} 
Output: bye 

Questions


1. WAP to find given number is positive or negative. 

Answer :  

class HelloWorld {
    public static void main(String[] args) {
        int number = -100;
        if(number<0){
            System.out.println("negative");
        }
        else{
            System.out.println("positive");
        }
    }
}


Q2. WAP to find greatest number among entered 2 integer values .

Answer : 

class HelloWorld {
    public static void main(String[] args) {
        int number_1 = 25;
        int number_2 = 20;
        if(number_1>number_2){
            System.out.println("number_1 is greater than number_2");
        }
        else{
            System.out.println("number_2 is greater than number_1");
        }
    }
}

Q3. WAP to determine given number is even or odd .

Answer : 

class HelloWorld {
    public static void main(String[] args) {
        int n = 20;
        if(n%2==0){
            System.out.println("number is even");
        }
        else{
            System.out.println("number is odd");
        }
    }
}
Switch statement

  • The if-else statement allows us to run a block of code among multiple alternative.
  • Instead of writing many if-else statements, you can use the switch statement.
  • The advantage of using a switch statement is that it make our code more readable.
Syntax : 
    switch (expression)
    {
        case value_1:
                 code statement;
                  break;
       case value_2:
                code statement;
                break;
                 |
                 |
                V
       case value_n:
                code statement;
                break;
       default :
                 default code;
    }
  • The default keyword specifies some code to run if there is no case match.
Example :
Calculator

public static void main(String[] args)
{

        Scanner sc = new Scanner(System.in);

      System.out.println("a = ");

        double a = sc.nextDouble();

        System.out.println("press the operator below");

        System.out.println(" +, "+" -, "+" *, "+" / ");

        char operator = sc.next().charAt(0);

        System.out.println("b = ");

        double b = sc.nextDouble();

        switch(operator){
            case'+':
                System.out.println("answer = "+ (a+b));
                break;
            case '-':
                System.out.println("answer = "+ (a-b));
                break;
            case '*':
                System.out.println("answer = "+ (a*b));
                break;
            case '/':
                System.out.println("answer = "+ (a/b));
                break;
            default:
                System.out.println("Invalid operator");
               
        }       
  }
  1. char operator = sc.next().charAt(0); -
This line of code reads a token from the input and extracts the first character from that token, storing it in the operators variable of type.

  • Flowchart : 



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