C Program sum of first n natural nummbers

Check if a Number is Even or Odd in C

Given an integer input, the objective is to determine whether a number is even or odd using C programming.

An even number is completely divisible by 2, whereas an odd number leaves a remainder of 1 when divided by 2.

C Program to Find the Sum of First N Natural Numbers

Natural numbers are a sequence of positive numbers starting from 1. The sum of the first N natural numbers can be calculated using different methods.

Method 1: Using for Loop

In this method, we iterate from 1 to N, adding each number to the sum variable.

#include <stdio.h>
int main() {
    int n, sum = 0;
    scanf("%d", &n);
    for(int i = 1; i <= n; i++)
        sum += i;
    printf("Sum is %d", sum);
    return 0;
}
            

Output:

5
Sum is 15

Explanation:

To calculate the sum of the first N natural numbers:

• Initialize a variable sum to 0.
• Use a for loop to iterate from 1 to N.
• Add each iterated value to the sum variable.
• Print the final sum.

Method 2: Using Formula

We use the mathematical formula: Sum = N * (N + 1) / 2 to compute the sum efficiently.

#include <stdio.h>
int main() {
    int n;
    scanf("%d", &n);
    int sum = n * (n + 1) / 2;
    printf("The sum is %d", sum);
    return 0;
}
            

Output:

6
The sum is 21

Explanation:

Using the formula N(N+1)/2, we can compute the sum in constant time:

• Substitute N with the given number.
• Compute the formula.
• Print the final sum.

This approach has a time complexity of O(1), making it highly efficient.

Method 3: Using Recursion

We use a recursive function that repeatedly adds numbers from N to 1.

#include <stdio.h>
int getSum(int n) {
    if(n == 0) return 0;
    return n + getSum(n - 1);
}
int main() {
    int n;
    scanf("%d", &n);
    printf("%d", getSum(n));
    return 0;
}
            

Output:

5
Sum is 15

Explanation:

To calculate the sum recursively:

• Define a recursive function getSum() that calls itself.
• Base case: If n == 0, return 0.
• Otherwise, return n + getSum(n-1).
• Print the result.

While recursion simplifies the code, it has a time complexity of O(N) and uses extra memory due to function calls.