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If-Else Statement in C

The if-else statement in C is used for decision-making. It allows the program to execute a block of code when a specified condition is true and a different block when the condition is false.

Flowchart:-

Syntax:

if (condition) {
    // Code to execute if the condition is true
} else {
    // Code to execute if the condition is false
}
Example 1: Check if a Number is Even or Odd
#include <stdio.h>
int main() {
    int num;

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

    if (num % 2 == 0) {
       printf("%d is even.\\n", num);
    } else {
       printf("%d is odd.\\n", num);
    }

    return 0;
}

Output:

Enter a number: 10
10 is even.
Example 2: Check if a Person is Eligible to Vote

In this example, we check whether a person is eligible to vote based on their age. A person is eligible to vote if their age is 18 or above.

#include <stdio.h>
int main() {
     int age;

     printf("Enter your age: ");
     scanf("%d", &age);

     if (age >= 18) {
         printf("You are eligible to vote.\n");
     } else {
         printf("You are not eligible to vote.\n");
     }

     return 0;
}

Output:

Enter your age: 20
You are eligible to vote.

If-Else-If Statement in C

As above following examples, the if code is printed when the condition is true and the else code is printed when the condition is false.

But what if, we want multiple conditions? There we use If-Else-If to work on multiple conditions.

Flowchart:-

Syntax:

if (condition) {
    // Code to execute if the condition is true
} else if (condition){
    // Code to execute if the condition is true
} else {
    // Code to execute if the condition is false
}
Example 3: Check Positive, Negative, or Zero
#include <stdio.h>
int main() {
    int num;

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

    if (num > 0) {
       printf("The number is positive.\\n");
    } else if (num < 0) {
       printf("The number is negative.\\n");
    } else {
       printf("The number is zero.\\n");
    }

    return 0;
}

Output:

Enter a number: -5
The number is negative.

Explanation :

In the first condition if the number is greater than zero then it will print.

If the number is not greater than zero then it will go onto the else-if to check whether the number is less than zero.

If number is not greater than zero nor less then all the condition will be false and the else code will be printed.

Example 4: Check Grade according to given marks.

This program checks the grade of a student based on marks entered by the user, using if-else if statements and logical operators.

#include <stdio.h>
int main() {
     int marks;

     printf("Enter your marks (0-100): ");
     scanf("%d", &marks);

     if (marks >= 90 && marks <= 100) {
         printf("Grade: A");
     } else if (marks >= 80 && marks < 90) {
         printf("Grade: B");
     } else if (marks >= 70 && marks < 80) {
         printf("Grade: C");
     } else if (marks >= 60 && marks < 70) {
         printf("Grade: D");
     } else if (marks >= 0 && marks < 60) {
         printf("Grade: F (Fail)");
     } else {
         printf("Invalid marks entered! Please enter a value between 0 and 100.");
     }
return 0;
}

Output:

Enter your marks: 85
Grade: B

Enter your marks: 150
Invalid marks entered! Please enter a value between 0 and 100.