C Program to find Sum of First n Natural numbers (4 ways)

By | August 28, 2020
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In this article, you will learn to calculate Sum of First n Natural numbers.

The positive numbers 1, 2, 3… are known as natural numbers. The sum of natural numbers up to 10 is:

sum = 1 + 2 + 3 + ... + 10

Find the sum of numbers for every number from 1 to 4 :

Sum of numbers till 1 = 1
Sum of numbers till 2 = 1 + 2 = 3
Sum of numbers till 3 = 1 + 2 + 3 = 6
Sum of numbers till 4 = 1 + 2 + 3 + 4 = 10

Implementation :

1. Using for loop :

// C Program to find Sum of N Numbers using For Loop 
#include<stdio.h>

int main()
{
    // take input
  int Number = 10 ;
  
  // intialze sum to 0
  int i, Sum = 0;
  for(i = 1; i <= Number; i++)
  {
      // sum with previous sum
     Sum = Sum + i;
  }
  
  printf("Sum of Natural Numbers til given number is = %d", Sum);
  
  // successful completion
  return 0;
}

Output :

Sum of Natural Numbers til given number is = 55

Note that you can use ‘while loop’ and ‘do while loop’ in place of ‘for loop’.

2. Using Mathematical formula :

// Using mathemamtical formula
#include <stdio.h>

int main() {
    
    // take input
   int n = 10;
   
   // calculate sum using mathematical formula
   int sum = (n*(n+1))/2;
   
   printf("Sum of Natural Numbers til given number is = %d", sum);
  
  // successful completion
  return 0;
}

Output :

Sum of Natural Numbers til given number is = 55

Note that mathematical formula to find the sum of sum of n natural number :

sum = n*(n+1)/2

3. Using Functions :

// C Program to find Sum of N Numbers using Functions 
#include<stdio.h>

// function of sum
int Sumof(int Number)
{
	
	 // intialze sum to 0
  int i, sum = 0;
  for(i = 1; i <= Number; i++)
  {
      // sum with previous sum
     sum = sum + i;
  }	
	return sum ;	
} ;

// driver code
int main()
{
    // take input
  int Number = 10 ;
  
  int result = Sumof(Number);
  
  printf("Sum of Natural Numbers til given number is = %d", result);
  
  // successful completion
  return 0;
}

Output :

Sum of Natural Numbers til given number is = 55

4. Using Recursion :

// C Program to find Sum of N Numbers using Functions 
#include<stdio.h>


// recursive function of sum
int Sumof(int Number)
{
    // base condition
	if (Number == 0) return Number;
	
	else 
	// for big numbers
	return (Number + Sumof(Number - 1));

} ;

// driver code
int main()
{
    // take input
  int Number = 10 ;
  
  int result = Sumof(Number);
  
  printf("Sum of Natural Numbers til given number is = %d", result);
  
  // successful completion
  return 0;
}

Output :

Sum of Natural Numbers til given number is = 55



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