# C Program to find Sum of N Numbers

How to write a C Program to find Sum of N Numbers using For Loop, While Loop, Do While Loop, Functions, and Recursion.

## C Program to find Sum of N Numbers using For Loop

This C program allows the user to enter any integer value. By using the For loop, this program calculates the sum of N natural numbers.

```#include<stdio.h>
int main()
{
int Number, i, Sum = 0;

scanf("%d", &Number);

for(i = 1; i <= Number; i++)
{
Sum = Sum + i;
}

printf("Sum of Natural Numbers = %d", Sum);
return 0;
}```

ANALYSIS:

• In this sum of n numbers program, the first printf statement will ask the user to enter an integer value. And the scanf statement will assign the user entered value to a Number variable.
• Next, we used C Programming For Loop to iterate between 1 and user-entered value. If you don’t know the For Loop, then please refer For loop in C Programming article for further reference.
• Within the For loop, we calculated the sum
• In the above C program example, user-entered value is 5 it means, 1 + 2 + 3 + 4 + 5 = 15

## C Program to find Sum of N Numbers using While Loop

This program for the sum of n numbers allows the user to enter any integer value. Using the While Loop, we will calculate the sum of N natural numbers.

```#include<stdio.h>
int main()
{
int n, i = 1, Sum = 0;

scanf("%d", &n);

while(i <= n)
{
Sum = Sum + i;
i++;
}

printf("Sum of Natural Numbers = %d", Sum);
return 0;
}```
``````Please Enter any Integer Value
5
Sum of Natural Numbers = 15``````

Within this C Program to find Sum of N Numbers using while loop example,

• While loop used to iterate between 1 and user-entered value. If you don’t know the While Loop, then please refer to While Loop in C article for further reference.
• Within the while loop, we calculated the sum
• After completing this, the value of i is increment by the Increment operator.

## C Program to Calculate Sum of N Numbers using Do While Loop

This sum of n numbers program allows the user to enter any integer value. Using the Do While Loop, we will calculate the sum of N natural numbers.

```#include<stdio.h>
int main()
{
int n, i = 1, Sum = 0;

scanf("%d", &n);

do
{
Sum = Sum + i;
i++;
} while(i <= n);

printf("Sum of Natural Numbers = %d", Sum);
return 0;
}```
``````Please Enter any Integer Value
50
Sum of Natural Numbers = 1275``````

We just replaced the While loop in the above Sum of N Numbers program with the Do While loop. Please don’t forget to miss the semi-colon after the while condition.

## C Program to find Sum of N Numbers using Functions

This sum of n numbers in c program allows the user to enter any integer value. Using the Functions, we will calculate the sum of N natural numbers.

```#include<stdio.h>
int SNatNum(int nm);

int main()
{
int nm, Sum = 0;

scanf("%d", &nm);

Sum = SNatNum(nm);

printf("Sum of Natural Numbers = %d", Sum);
return 0;
}

int SNatNum(int nm)
{
int Sum = 0;

if (nm == 0)
{
return nm;
}
else
{
return (nm * (nm + 1) / 2);
}

}```
``````
100
Sum of Natural Numbers = 5050``````

Within this C Program to find the Sum of N Numbers, the following statement will call the SNatNum function and assign the function return value to the Sum variable.

`Sum = SNatNum(nm);`

The last printf statement will print the Sum as output. Now, let us see the function definition

Within the function, we used the If Else statement checks whether the Number is equal to Zero or greater than Zero.

• If the given number is equal to Zero then Sum of N Natural numbers = 0
• Otherwise, we used the mathematical formula of Sum of Series 1 + 2+ 3+ … + N = N * (N + 1) / 2

## C Program to find Sum of N Numbers using Recursion

This program to find the sum of n numbers allows the user to enter any integer value. Using the Recursion, we will calculate the sum of N natural numbers.

```#include<stdio.h>
int SNatNum(int nb);

int main()
{
int nb, Sum = 0;

scanf("%d", &nb);

Sum = SNatNum(nb);

printf("Sum of Natural Numbers = %d", Sum);
return 0;
}
int SNatNum(int nb)
{
if (nb == 0)
{
return nb;
}
else
{
return (nb + SNatNum(nb - 1));
}
}```
``````Please Enter any Integer Value
1000
Sum of Natural Numbers = 500500``````

If you observe the above Program to calculate the Sum of N Numbers code, it is very similar to the code we explained in the Functions concept. But within the else statement, we called the function recursively.

`return (Number + SNatNum(nb - 1));`