C if...else Statement

In this tutorial, you will learn about if statement (including if...else and nested if..else) in C programming with the help of examples.

C if Statement

The syntax of the if statement in C programming is:

if (test expression)

{

   // statements to be executed if the test expression is true

}

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How if statement works?

The if statement evaluates the test expression inside the parenthesis ().

·       If the test expression is evaluated to true, statements inside the body of if are executed.

·       If the test expression is evaluated to false, statements inside the body of if are not executed.

To learn more about when test expression is evaluated to true (non-zero value) and false (0), check relational and logical operators.

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Example 1: if statement

// Program to display a number if it is negative

 

#include <stdio.h>

int main() {

    int number;

 

    printf("Enter an integer: ");

    scanf("%d", &number);

 

    // true if number is less than 0

    if (number < 0) {

        printf("You entered %d.\n", number);

    }

 

    printf("The if statement is easy.");

 

    return 0;

}

Output 1

Enter an integer: -2

You entered -2.

The if statement is easy.

When the user enters -2, the test expression number<0 is evaluated to true. Hence, You entered -2 is displayed on the screen.

Output 2

Enter an integer: 5

The if statement is easy.

When the user enters 5, the test expression number<0 is evaluated to false and the statement inside the body of if is not executed

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C if...else Statement

The if statement may have an optional else block. The syntax of the if..else statement is:

if (test expression) {

    // statements to be executed if the test expression is true

}

else {

    // statements to be executed if the test expression is false

}

---

How if...else statement works?

If the test expression is evaluated to true,

·       statements inside the body of if are executed.

·       statements inside the body of else are skipped from execution.

If the test expression is evaluated to false,

·       statements inside the body of else are executed

·       statements inside the body of if are skipped from execution.

---

Example 2: if...else statement

// Check whether an integer is odd or even

 

#include <stdio.h>

int main() {

    int number;

    printf("Enter an integer: ");

    scanf("%d", &number);

 

    // True if the remainder is 0

    if  (number%2 == 0) {

        printf("%d is an even integer.",number);

    }

    else {

        printf("%d is an odd integer.",number);

    }

 

    return 0;

}

Output

Enter an integer: 7

7 is an odd integer.

When the user enters 7, the test expression number%2==0 is evaluated to false. Hence, the statement inside the body of else is executed.

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C if...else Ladder

The if...else statement executes two different codes depending upon whether the test expression is true or false. Sometimes, a choice has to be made from more than 2 possibilities.

The if...else ladder allows you to check between multiple test expressions and execute different statements.

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Syntax of if...else Ladder

if (test expression1) {

   // statement(s)

}

else if(test expression2) {

   // statement(s)

}

else if (test expression3) {

   // statement(s)

}

.

.

else {

   // statement(s)

}

---

Example 3: C if...else Ladder

// Program to relate two integers using =, > or < symbol

 

#include <stdio.h>

int main() {

    int number1, number2;

    printf("Enter two integers: ");

    scanf("%d %d", &number1, &number2);

 

    //checks if the two integers are equal.

    if(number1 == number2) {

        printf("Result: %d = %d",number1,number2);

    }

 

    //checks if number1 is greater than number2.

    else if (number1 > number2) {

        printf("Result: %d > %d", number1, number2);

    }

 

    //checks if both test expressions are false

    else {

        printf("Result: %d < %d",number1, number2);

    }

 

    return 0;

}

Output

Enter two integers: 12

23

Result: 12 < 23

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Nested if...else

It is possible to include an if...else statement inside the body of another if...else statement.

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Example 4: Nested if...else

This program given below relates two integers using either <, > and = similar to the if...else ladder's example. However, we will use a nested if...else statement to solve this problem.

#include <stdio.h>

int main() {

    int number1, number2;

    printf("Enter two integers: ");

    scanf("%d %d", &number1, &number2);

 

    if (number1 >= number2) {

      if (number1 == number2) {

        printf("Result: %d = %d",number1,number2);

      }

      else {

        printf("Result: %d > %d", number1, number2);

      }

    }

    else {

        printf("Result: %d < %d",number1, number2);

    }

 

    return 0;

}

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If the body of an if...else statement has only one statement, you do not need to use brackets {}.

For example, this code

if (a > b) {

    print("Hello");

}

print("Hi");

is equivalent to

if (a > b)

    print("Hello");

print("Hi");