C Decision Making: If, If-Else, Switch-Case

In this C programming class, we’ll cover the C decision-making constructs such as C if, if-else, and the switch-case statement. It is also known as conditional programming in C.

In your life, you encounter situations where you have to make a decision be it your favorite food dish or the color of your new car. In C programming also, you may encounter such situations where you need to make a decision.

The conditions in C language will help you. C primarily provides the following three types of conditional or decision-making construct.

Don’t miss out on how to write your first C program in just 2 minutes.

If Statement in C

The if statement helps you check a particular condition. If that condition is true, then a specific block (enclosed under the if) of code gets executed.

This flowchart will help you.

C If Syntax:

if(condition either true or false)
{
    //Statement block
}

Now we will see a simple program using an if statement.

Program using C If Statement to Find the Greatest of Two Numbers.

Flowchart:

Algorithm:

Step 1: Start.

Step 2: Take two inputs (a and b) from the user.

Step 3: If a is greater than b then go to step 4 otherwise go to step 5

Step 4: Print a greater than b

Step 5: Print b greater than a

Step 6: Stop.

Code:

#include<stdio.h>
#include<conio.h>

void main()
{
    int a,b;

    printf("Enter two numbers :");
    scanf("%d %d",&a,&b);

    if (a>b)
        printf("%d is greater",a);

    printf("%d is greater",b);

    getch();
}

The output is as follows:

If…Else Statement in C

The if statement works pretty well, but if you want to work with more variables and more data, the if-else statement comes into play.

In the if statement, only one block of code executes after the condition is true.

But in the if-else statement, there are two blocks of code – one for handling the success and the other for the failure condition.

This flowchart will help you get it.

C If…Else Syntax:

if(condition)
{
    //Statement block
}
else
{
    //Statement block
}

Program using C If…Else to Find Whether a Number is Odd or Even.

Flowchart:

Algorithm:

Step 1: Start.

Step 2: Take input from the user.

Step 3: Check condition. If remainder is zero go to step 4 else go to step 5

Step 4: Print a is even and go to step 6

Step 5: Print a is odd

Step 6: Stop

Code:

#include<stdio.h>
#include<conio.h>

void main()
{
    int a;

    printf("Enter a number :");
    scanf("%d",&a);

    if (a%2==0)
    {
        printf("%d is even",a);
    }
    else
        printf("%d is odd",a);

    getch();
}

The output should look something like this-

You can use multiple if-else statements which get called “nested if-else” statements. It is no different than the one above you can use various if-else statements in this order. Just keep in mind that the sequence should end with a final else statement, not an if statement.

Switch-Case Statement in C

When you have to execute multiple statements under one operation, Switch-case comes into play.

There are several cases under one switch statement.

C Switch…Case Syntax:

switch(variable)
{
    case n1:
        //Statement block;
        break;
    case n2:
        //Statement block;
        break;
    .
    .
    .
    case n:
        //Statement block;
        break;
}

Here the variable is taken from the user as input.

Program using C Switch…Case to Calculate the Area of a Rectangle/Circle/Triangle.

Flowchart:

Algorithm:

Step 1: Start

Step 2: Initialize variables

Step 3: Take input for choice and then for area variables from the user

Step 4: Case 1: Circle: 3.14*3.14*r

Case 2: Rectangle: ar=a*b

Case 3: Triangle: at=0.5*a*b

Step 5: Display output according to case

Step 6: Stop

Code:

#include<stdio.h>
#include<conio.h>

void main()
{
    int ac,ar,at,r,a,b,choice;

    printf("Enter your choice\n”);
    prinft(“A for area of circle\n”);
    printf(“B for area of rectangle\n”);
    printf(“C for area of triangle\n");
    scanf("%c",&choice);

    switch(choice)
    {
    case A:
        printf("Enter radius: ");
        scanf("%d",&r);
        ac=3.14*3.14*r;
        printf("Area of circle is: %d",ac);
        break;
    case B:
        printf("Enter length and breadth:");
        scanf("%d %d",&a,&b);
        ar=a*b;
        printf("Area of rectangle is: %d",ar);
        break;
    case C:
        printf("Enter base and height: ");
        scanf("%d %d",&a,&b);
        at=0.5*a*b;
        printf("Area of triangle is: %d",at);
        break;
    }

    getch();
}

Output: