C Program to Check Voting Eligibility

A C program to check voting eligibility reads the user's age using scanf and uses an if statement to print "Eligible to vote" if age is 18 or above, otherwise "Not eligible to vote".

Examples

Input20

OutputEligible to vote

Input17

OutputNot eligible to vote

Input18

OutputEligible to vote

How to Think About It

To check voting eligibility, first get the person's age. Then compare the age with 18 using the >= operator. If the age is 18 or more, the person can vote; otherwise, they cannot.

Algorithm

1

Get the user's age as input

2

Check if age is greater than or equal to 18

3

If yes, print "Eligible to vote"

4

Otherwise, print "Not eligible to vote"

Code

c

#include <stdio.h>

int main() {
    int age;
    printf("Enter your age: ");
    scanf("%d", &age);
    if (age >= 18) {
        printf("Eligible to vote\n");
    } else {
        printf("Not eligible to vote\n");
    }
    return 0;
}

Output

Enter your age: 20
Eligible to vote

Dry Run

Let's trace the input age 20 through the code

1

Input age

User enters age = 20

2

Check age >= 18

20 >= 18 is true

3

Print result

Print "Eligible to vote"

Age	Condition (age >= 18)	Output
20	true	Eligible to vote

Why This Works

Step 1: Reading input

The program uses scanf to get the user's age from the keyboard.

Step 2: Decision making

It uses an if statement to check if the age is 18 or more with age >= 18.

Step 3: Output result

If the condition is true, it prints "Eligible to vote"; otherwise, it prints "Not eligible to vote".

Alternative Approaches

Using ternary operator

c

#include <stdio.h>

int main() {
    int age;
    printf("Enter your age: ");
    scanf("%d", &age);
    age >= 18 ? printf("Eligible to vote\n") : printf("Not eligible to vote\n");
    return 0;
}

This approach uses a shorter syntax with the ternary operator but may be less clear for beginners.

Using function to check eligibility

c

#include <stdio.h>

int isEligible(int age) {
    return age >= 18;
}

int main() {
    int age;
    printf("Enter your age: ");
    scanf("%d", &age);
    if (isEligible(age)) {
        printf("Eligible to vote\n");
    } else {
        printf("Not eligible to vote\n");
    }
    return 0;
}

This approach separates logic into a function, improving readability and reusability.

Complexity: O(1) time, O(1) space

Time Complexity

The program performs a single comparison operation, so it runs in constant time O(1).

Space Complexity

Only a few variables are used, so space complexity is constant O(1).

Which Approach is Fastest?

All approaches run in constant time; using a function adds slight overhead but improves code structure.

Approach	Time	Space	Best For
If-else statement	O(1)	O(1)	Simple and clear logic
Ternary operator	O(1)	O(1)	Shorter code, less readable for beginners
Function-based check	O(1)	O(1)	Better code organization and reuse