Write a C program to find sum of all prime numbers between 1 to n using for loop. C program to generate sum of all primes between a given range. Logic to find sum of prime numbers in a given range.

**Example**

**Input**

Input upper limit: 10

**Output**

Sum of prime numbers between 1-10: 17

## Required knowledge

Basic C programming, If else, For loop, Nested loops

## What is Prime number?

Prime numbers are the positive integers greater than 1 that has only two divisors 1 and the number itself. For example: 2, 3, 5, 7, 11 are the first 5 prime numbers.

## Logic to find sum of prime numbers between 1 to n

Finding sum of prime number is just a 7 std kid task, if you know checking prime numbers. Before I get to the formal logic of the program. I recommend you to learn the below two concepts before moving on.

Below is the step by step descriptive logic to find sum of prime numbers between 1 to n.

- Read upper limit to find sum of prime from user. Store it in some variable say n.
- Initialize another variable sum = 0 to store sum of prime numbers.
- Run a loop from 2 to n, incrementing 1 in each loop counter. The loop structure should look like for(i=2; i<=n; i++).
- Inside this loop check if i is prime. Then increment the sum variable by 1 i.e. sum = sum + 1.
- Finally after loop print the resultant value of sum.

## Program to find sum of prime numbers between 1 to n

/** * C program to find sum of prime numbers between 1 to n */ #include <stdio.h> int main() { int i, j, n, isPrime, sum=0; /* * Read upper limit from user */ printf("Find sum of all prime between 1 to : "); scanf("%d", &n); /* * Find all prime numbers between 1 to n */ for(i=2; i<=n; i++) { /* * Check if the current number i is Prime or not */ isPrime = 1; for(j=2; j<=i/2 ;j++) { if(i%j==0) { isPrime = 0; break; } } /* * If i is Prime then add to sum */ if(isPrime==1) { sum += i; } } printf("Sum of all prime numbers between 1 to %d = %d", n, sum); return 0; }

## Program to find sum of prime numbers in given range

/** * C program to find sum of prime numbers in given range */ #include <stdio.h> int main() { int i, j, start, end; int isPrime, sum=0; /* * Read lower and upper limit from user */ printf("Enter lower limit: "); scanf("%d", &start); printf("Enter upper limit: "); scanf("%d", &end); /* * Find all prime numbers in given range */ for(i=start; i<=end; i++) { /* * Check if the current number i is Prime or not */ isPrime = 1; for(j=2; j<=i/2 ;j++) { if(i%j==0) { isPrime = 0; break; } } /* * If i is Prime then add to sum */ if(isPrime==1) { sum += i; } } printf("Sum of all prime numbers between %d to %d = %d", start, end, sum); return 0; }

Enter lower limit: 10 Enter upper limit: 20 Sum of all prime numbers between 10 to 20 = 60

Happy coding ;)

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