Sum of N Natural Numbers in C

Flow Control
If-else Statement in C
Programs on if-else
Switch Case in C
Switch case Programs
Conditional Operator
While loop in C
Do-while loop in C
While vs do-while
For loop in C
Break keyword in C
Continue keyword in C
Break vs Exit in C
Goto keyword in C
☕️ Flow Control Programs
Largest in 3 Numbers
Find Grade of student
Find the absolute value
Vowel or Consonant
Leap Year Program
Simple calculator in C
Check Odd or Even 
Roots of Quadratic Equation
Find Reverse of Number
Factors of a number in C
Generate Multiplication table
Find Power of a Number
Find GCD and LCM
Find factorial of Number
Count Number of Digits
Sum of digits in Number
Sum of N Natural Numbers
Sum of Squares of Natural No.
Find Sum of Odd Numbers
Find the Sum of Series
Find Fibonacci series in C
Sum of the Fibonacci series
Sum until enters +ve numbers
Sum of max 10 no. & Skip -ve
☕️ C Conversion Programs
Celsius to Fahrenheit
Fahrenheit to Celsius
Decimal ↔ Binary
Decimal ↔ Octal
Octal ↔ Binary in C
☕️ Number Programs in C
Prime Number in C
Strong Number in C
Krishnamurthy Number
Neon Number in C
Palindrome number
Perfect Number in C
Armstrong Number
☕️ Pattern Programs in C
Pattern programs in C
Printing pattern using loops
Floyd’s triangle Program
Pascal Triangle Program
Pyramid Star Pattern in C
Diamond Pattern Programs
Half Diamond pattern in C
Print Diamond Pattern
Hollow Diamond Pattern
Diamond Pattern of Numbers

Write a C program to find the sum of N natural numbers in C using for loop, while loop, do-while loop, and without loop. Prerequisites:- While loop in C, Do-while loop in C, Difference between while and do-while, For loop in C

Sum of natural number N as given as sum = 1+2+3+….+N

Examples:-
1+2+3+4+5 = 15
1+2+3+4+5+6+7+8+9+10 = 55

To find the sum of natural numbers declare a variable and initialize it with value 1. Declare another variable sum and initialize it with 0. Now, in every iteration increase sum value until the value N.

Sum of N Natural Numbers in C using for loop

#include<stdio.h>
int main()
{
  int n, sum=0;

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

  for(int i=0; i<=n; i++)
  {
    sum += i; //sum = sum + i
  }

  printf("Sum of first %d natural numbers = %d",
                                       n, sum );

  return 0;
}

Output for the different test-cases:-

Enter n value: 10
Sum of first 10 natural numbers = 55

Enter n value: 0
Sum of first 0 natural numbers = 0

The sum of N natural numbers also can be calculated in reverse order. For example The sum of 5 natural numbers= 5+4+3+2+1

In this case, the loop control variable should initialize with “n” and the decrement operator should be used. The below program shows it,

#include<stdio.h>
int main()
{
  int n, sum=0;

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

  for(int i=n; i>=0; i--)
  {
    sum += i;
  }

  printf("Sum of first %d natural numbers = %d",
                                      n, sum );

  return 0;
}

Using While Loop

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

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

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

  printf("Sum of first %d natural numbers = %d",
                                       n, sum);

  return 0;
}

The statements of the while loop given in this program can be also written as given below,

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

Using the do-while loop

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

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

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

  printf("Sum of first %d natural numbers = %d",
                                      n, sum );

  return 0;
}

The time complexity for all above program was O(n).

Sum of N natural numbers in C without loop

We can also do the same work without using the loop. The formula for this operation,

sum = n*(n+1)/2;

Example:-
Sum of first 10 natural numbers = 10*(10+1)/2 = 10*11/2 = 5*11 = 55

#include<stdio.h>
int main()
{
  int n, sum;

  printf("Enter a positive number: ");
  scanf("%d", &n);

  sum = n*(n+1)/2;

  printf("Sum = %d", sum);

  return 0;
}

Output for the different cases:-

Enter a positive number: 10
Sum = 55

Enter a positive number: 15
Sum = 120

The time complexity for this program is O(1).

We can do the same task using Recursion also:- Find the sum of Natural number using recursion

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Flow Control
If-else Statement in C
Programs on if-else
Switch Case in C
Switch case Programs
Conditional Operator
While loop in C
Do-while loop in C
While vs do-while
For loop in C
Break keyword in C
Continue keyword in C
Break vs Exit in C
Goto keyword in C
☕️ Flow Control Programs
Largest among 3 Numbers
Find Grade of student
Find the absolute value
Check Vowel or Consonant
Leap Year Program
Simple calculator in C
Check Odd or Even 
Roots of Quadratic Equation
Find Reverse of Number
Factors of a number in C
Generate Multiplication table
Find Power of a Number
Find GCD and LCM
Find factorial of Number
Count Number of Digits
Sum of digits in Number
Sum of N Natural Numbers
Sum of Squares of Natural No.
Find Sum of Odd Numbers
Find the Sum of Series
Find Fibonacci series in C
Sum of the Fibonacci series
Sum until enters +ve numbers
Sum of max 10 no. & Skip -ve
☕️ C Conversion Programs
Celsius to Fahrenheit
Fahrenheit to Celsius
Decimal ↔ Binary
Decimal ↔ Octal
Octal ↔ Binary in C
☕️ Number Programs in C
Prime Number in C
Strong Number in C
Krishnamurthy Number
Neon Number in C
Palindrome number
Perfect Number in C
Armstrong Number
☕️ Pattern Programs in C
Pattern programs in C
Printing pattern using loops
Floyd’s triangle Program
Pascal Triangle Program
Pyramid Star Pattern in C
Diamond Pattern Programs
Half Diamond pattern in C
Print Diamond Pattern
Hollow Diamond Pattern
Diamond Pattern of Numbers

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