Conditional Construct

if statement

---

The if statement in java tests the condition. It executes the statement inside if block if condition is true.

Syntax :

if(condition){ 
    
    
    //statements
    
    

    }

Example :

Output :

if-else statement

---

The if-else statement in java also tests the condition. if condition is true it executes the statement inside if block otherwise the statement inside else block is executed .

Syntax :

if(condition){ 

    //statements

    }

    else

    { 

    //statements 

    }

Example :

Output :

nested-if statement

---

The nested if statement contains if block within another if block. The inner if block executes only when outer if block condition is true.

Syntax :

if(condition)
{
    //statements

         if(condition)
         {  
            //statements 
         }    
} 

Example :

Output :

if-else-if ladder statement

---

It is used when multiple decisions are involved and in this along with if statement each else if construct is used.

Syntax :

if(condition1)

{  
    //statements to be executed if condition1 is true  

}
    else if(condition2)
{ 

    //statements to be executed if condition2 is true 

}  
    else if(condition3)
{ 

    //statements to be executed if condition3 is true   
    
}  
...
...  
    
else
{  
    
    //statements to be executed if all the conditions are false  
    
} 

Example :

Output :

Switch-Case

---

Switch case is one of the conditional statement which is found in most of the programming languages

In this if we have more than one choices,and we have to select one of the choice then we use switch case.The choice is selected based on the value of expression.The expression can be a byte,short,char and int primitive datatype

It does not support the conditional operators(which are >,<,>=,<=,etc), like the if-else statement can,nor it can handle multiple variables

Syntax:



In the above syntax,when any of the case will be true,then the statement inside it will be executed and break statement will be applied.After that this process won't be executed further,it will move out of the switch case.

When condition does not match with any of the case,it will run default case.

Example:



Here "num" is the variable to be compared and if we input num as 3,then the output will be

Enter the number
3
Three

this means that case3 will be executed,after that this switch statment will be terminated.

Fall-through in Switch case

---

In switch case,when there is no break commands mentioned in the particular case and cause execution of the cases until it finds any break statement,then such statments is called fall through statement.

If there is no break statement till the end then default statements will be executed.

Let us understand this by an example:



In the above program ,if we input n as 1 then all the cases till default case will be executed.So the output will be:

This is
the
fallthrough
Statement

Difference in switch and if-else statement

---

Switch case:

• In switch case,it check only double assignment(==) operator,no other relational or logical operator is used.
• Here the datatypes that we can use in conditions are int and char only

If else:

• In if-else statement,all the logical,relational and assignment operator is used
• Here the datatype which can be used in condition are int,char,string,double,etc.

Menu-driven Programs

---

Example : 1 Write a menu driven program to print the area of different geometrical shapes as given below :

Choice	Shape
1	Right Triangle
2	Equilateral triangle
3	Square
4	Rectangle
5	Circle

import java.util.*;
class Menu
{
public static void main(String[] args)
{
 int choice;
 double area;
 int l,b;
 int a;
 int r;
 Scanner sc = new Scanner(System.in);
 System.out.println("1- Area of Right Triangle");
 System.out.println("2- Area of Equilateral Triangle");
 System.out.println("3- Area of Square");
 System.out.println("4- Area of Rectangle");
 System.out.println("5- Area of Circle");
 System.out.println("------------------------------");
 System.out.print("Select your choice=");        
 choice = sc.nextInt();
 switch (choice)
 {
     case 1:
         System.out.print("Enter l=");
         l=sc.nextInt();
         System.out.print("Enter b=");
         b=sc.nextInt();
         area=(l*b)/2;
         System.out.println("Area of Right Triangle="+area);
         break;
     case 2:                
         System.out.print("Enter a=");
         a=sc.nextInt();
         area=(a*a*Math.sqrt(3))/4;
         System.out.println("Area of Equilateral Triangle="+area);
         break;
     case 3:
         System.out.print("Enter a=");
         a=sc.nextInt();
         area=a*a;
         System.out.println("Area of Square="+area);
         break;
     case 4:
         System.out.print("Enter l=");
         l=sc.nextInt();
         System.out.print("Enter b=");
         b=sc.nextInt();
         area=l*b;
         System.out.println("Area of Rectangle="+area);
         break;
     case 5:
         System.out.print("Enter r=");
         r=sc.nextInt();
         area=r*r*22/7;
         System.out.println("Area of Circle="+area);
         break;
     default:
         System.out.print("Enter valid choice.");
 }
}
}
             
         
         

Output :

1- Area of Right Triangle
2- Area of Equilateral Triangle
3- Area of Square
4- Area of Rectangle
5- Area of Circle
------------------------------
Select your choice=1
Enter l=12
Enter b=12
Area of Right Triangle=72.0
         

Example : 2 Write a menu driven program to print the corresponding week day as per the input number as given below :

No.	Day
1	Monday
2	Tuesday
3	Wednesday
4	Thursday
5	Friday
6	Saturday
7	Sunday

import java.util.*;

public class NameOfDay
{
public static void main(String[] args)
{
    int day;
    Scanner sc=new Scanner(System.in);
    System.out.print("Enter day=");
    day=sc.nextInt();
    switch(day)
    {
        case 1:
            System.out.println("Monday");
            break;
        case 2:
            System.out.println("Tuesday");
            break;
        case 3:
            System.out.println("Wednesday");
            break;
        case 4:
            System.out.println("Thursday");
            break;
        case 5:
            System.out.println("Friday");
            break;
        case 6:
            System.out.println("Saturday");
            break;
        case 7:
            System.out.println("Sunday");
            break;
        default:
            System.out.println("Enter valid day.");                
    }
}
}
             
         
         

Output :

Enter day=5
Friday
         

Example : 3 Write a menu driven program to perform basic arithmetic operations as per the input number given below :

No.	Operation
1	Addition
2	Subtraction
3	Multiplication
4	Division
5	Quit

import java.util.*;
//Creating Class
class menu2 {
//Creating main method
public static void main(String[] args){

int a,b,c;
int choice;
Scanner scanner = new Scanner(System.in);
//Creating menu
System.out.println("Press 1 for Addition");
System.out.println("Press 2 for Subtraction");
System.out.println("Press 3 for Multiplication");
System.out.println("Press 4 for Division");
System.out.println("Press 5 to Quit\n \n ");
//Asking user to make choice
System.out.println("Make your choice");
choice = scanner.nextInt();

switch (choice) {
    //First case for finding the addition
    case 1:
        System.out.println("Enter the first number ");
        a = scanner.nextInt();
        System.out.println("Enter the second number");
        b = scanner.nextInt();
        c = a + b;
        System.out.println("The sum of the numbers is = " + c +"\n");
        break;
    //Second case for finding the difference
    case 2:
        System.out.println("Enter the first number ");
        a = scanner.nextInt();
        System.out.println("Enter the second number");
        b = scanner.nextInt();
        c = a - b;
        System.out.println("The difference of the numbers is = " + c +"\n");
        break;
    //Third case for finding the product
    case 3:
        System.out.println("Enter the first number");
        a = scanner.nextInt();
        System.out.println("Enter the second number");
        b = scanner.nextInt();
        c = a * b;
        System.out.println("The product of the numbers is = " + c + "\n");
        break;
    //Fourth case for finding the quotient
    case 4:
        System.out.println("Enter the first number");
        a = scanner.nextInt();
        System.out.println("Enter the second number");
        b = scanner.nextInt();
        c = a / b;
        System.out.println("The quotient is = " + c +"\n");
        break;
    //Fifth case to quit the program
    case 5:
        System.exit(0);
    //default case to display the message invalid choice made by the user
    default:
        System.out.println("Invalid choice!!! Please make a valid choice. \\n\\n");
}

}
}
                 
             
             

Output :

Press 1 for Addition
Press 2 for Subtraction
Press 3 for Multiplication
Press 4 for Division
Press 5 to Quit
    
    
Make your choice
1
Enter the first number 
12
Enter the second number
12
The sum of the numbers is = 24