Thread: Program to check whether given number is prime or not?

  1. #1
    Registered User
    Join Date
    Mar 2015

    Program to check whether given number is prime or not?

    Hi there, I've written a c program in answer to the following question:

    write a function prime that returns 1 if its argument is a prime number and 0 if it is otherwise.
    My code is:
    // write a program that returns 1 for prime number and 0 if not prime
    //source: stephen kochan, programming in C, chapter 8
    // function to check n is prime or not
    void prime (int n)
      int i, c = 0;
          for (i = 1; i <= n; i++) {
              if (n % i == 0) {
          if (c == 2) {
          else {
    int main (void)
      void prime (int n);
      int m;
     printf("Please Give a number to check whether prime or not\n");
     scanf("%i", &m);
     return 0;
    The issue is I'm only printing 1 or 0. How am I supposed to RETURN these values from the function? A little confused, any help would be appreciated.

  2. #2
    C++ Witch laserlight's Avatar
    Join Date
    Oct 2003
    Consider this function that returns 1:
    int foo(void)
        return 1;
    As you can see, it has a return type of int, and there is a return statement that returns 1. You would need to modify your prime function to be along these lines.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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