In this C program, we will find all prime numbers between 1 to N. A Prime number is a natural number greater than 1 that is only divisible by either 1 or itself.

All numbers other than prime numbers are known as composite numbers. There are infinitely many prime numbers, here is the list of first few prime numbers

2 3 5 7 11 13 17 19 23 29 31 37....

#### Required Knowledge

**Algorithm to check whether a number is prime number or not**

*Let, N be a positive number.*

- For every number i, between 2 to N/2(2<= i <= N/2) check whether i divides N completely(check If i is a factor of N).
- if (N % i == 0), then N cannot be a Prime number.
- If none of the number between 2 to N/2 divides N completely then N is a prime number.

## C program to print all prime numbers between 1 to N using for loop

#include<stdio.h> int main(){ int N, i, j, isPrime, n; printf("Enter the value of N\n"); scanf("%d",&N); printf("Prime numbers between %d to %d\n", 1, N); for(i = 2; i <= N; i++){ isPrime = 0; /* Check whether i is prime or not */ for(j = 2; j <= i/2; j++){ if(i % j == 0){ isPrime = 1; break; } } if(isPrime==0 && N!= 1) printf("%d ",i); } return 0; }Output

Enter the value of N 50 Prime numbers between 1 to 50 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47

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