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C Program to Check Whether a Number is Prime or Not



What is Prime number?

Prime number is a positive integer greater than 1 that is only divisible by 1 and itself. For example: 2, 3 , 5, 7, 11 are the first five prime numbers.

Logic to print prime numbers between 1 to n

Step by step descriptive logic to print all prime numbers between 1 to n.

  1. Input upper limit to print prime numbers from user. Store it in some variable say end.
  2. Run a loop from 2 to end, increment 1 in each iteration. The loop structure should be like for(i=2; i<=end; i++).
  3. Inside the loop for each iteration print value of i if it is prime number
/** * C program to print all prime numbers between 1 to n */ #include <stdio.h> int main() { int i, j, end, isPrime; // isPrime is used as flag variable /* Input upper limit to print prime */ printf("Find prime numbers between 1 to : "); scanf("%d", &end); printf("All prime numbers between 1 to %d are:\n", end); /* Find all Prime numbers between 1 to end */ for(i=2; i<=end; i++) { /* Assume that the current number is Prime */ isPrime = 1; /* Check if the current number i is prime or not */ for(j=2; j<=i/2; j++) { /* * If i is divisible by any number other than 1 and self * then it is not prime number */ if(i%j==0) { isPrime = 0; break; } } /* If the number is prime then print */ if(isPrime==1) { printf("%d, ", i); } } return 0; }

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