3 different C programs to find the sum of first n odd natural numbers

C program to find the sum of first n odd natural numbers:

This post will show you how to find the sum of first n odd natural numbers in C. The program will take the value of n as the input from the user and print the sum.

A number is called odd if it is not divisible by 2. Before we start writing the program, let’s learn the algorithm to use in the program.

Algorithm:

We have to use one loop to iterate from 1 to calculate the final sum.

We can use one loop and check for each value if it is an odd or even:

Run one loop from 1.
Initialize a sum variable as 0 to hold the final sum of all odd numbers. Initialize another variable as 0 to hold the total count of odd numbers found.
For each value, check if it is odd or even. If it is odd, add it to the sum variable.
If the count variable is equal to n, exit from the loop.
Once the loop ends, print the value of the sum variable.

We can also run a loop from 1 with an increment of 2 on each iteration. This will skip all even numbers and it will iterate only the odd values. We can add all numbers it is iterating to get the final sum.

Method 1: C program to find the sum of odd natural numbers by using a for loop:

Let’s write a program that uses a for loop to find the sum of first n odd numbers starting from 1. It will take the value of n as an input from the user.

#include <stdio.h>

int getOddSum(int n)
{
    int sum = 0, count = 0;

    for (int i = 1;; i++)
    {
        if (i % 2 != 0)
        {
            sum += i;
            count++;
        }
        if (count == n)
            break;
    }
    return sum;
}

int main()
{
    int n;

    printf("Enter the value value of n: ");
    scanf("%d", &n);

    printf("Sum of first %d odd numbers is: %d\n", n, getOddSum(n));
}

Here,

The program is asking the user to enter the value of n. This value is stored in the variable n.
It calls the getOddSum method to get the sum of the first n odd numbers starting from 1.
It uses a for loop that runs from 1 . On each iteration, it checks the value of i. If it is odd, it adds it to the variable sum.
It uses the count variable to hold the number odd variables added. Once it is equal to n, it breaks from the loop.
It returns the value of sum at the end.

If you run this program, it will give outputs as below:

Enter the value value of n: 10
Sum of first 10 odd numbers is: 100

Enter the value value of n: 2
Sum of first 2 odd numbers is: 4

Method 2: By incrementing 2 on each iteration:

We can change the above program to increment the value of i by 2 on each iteration. It will skip all even values and iterate only over the odd values.

#include <stdio.h>

int getOddSum(int n)
{
    int sum = 0, count = 0;

    for (int i = 1; count < n; i += 2)
    {
        sum += i;
        count++;
    }
    return sum;
}

int main()
{
    int n;

    printf("Enter the value value of n: ");
    scanf("%d", &n);

    printf("Sum of first %d odd numbers is: %d\n", n, getOddSum(n));
}

We don’t have to check if the current value of i is odd or even. We can add all the numbers in the loop. It will give similar results.

Enter the value value of n: 3
Sum of first 3 odd numbers is: 9

Method 3: By using a while loop:

We can also use a while loop to write the same program. It will increment the value of i by 2 similar to the above example.

#include <stdio.h>

int getOddSum(int n)
{
    int sum = 0, count = 1, i = 1;

    while (count <= n)
    {
        sum += i;
        i += 2;
        count++;
    }
    return sum;
}

int main()
{
    int n;

    printf("Enter the value value of n: ");
    scanf("%d", &n);

    printf("Sum of first %d odd numbers is: %d\n", n, getOddSum(n));
}

It will print similar output.

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Updated on 11 Apr 2022

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