CODEWITHSUNDEEP
c
Nasc
Nasc

Reputation: 65

What's wrong with my Checkprime.c program?

I'm trying to make a program that checks whether a given number is a prime number or not. However, my program just gives me the 2 time table, and I don't know why.

Here is my main class:

#include <stdio.h>
#include "defs.h"
#include "checkprime.c"


int Prime[MaxPrimes];  

int main()
{ 
  int UpperBound;
  int N;
  int *ba = &UpperBound;

  printf("enter upper bound\n");
  scanf("%d",ba);

  Prime[2] = 1;

  for (N = 3; N <= *ba; N+= 2)
  {
    CheckPrime(N);
    if (Prime[N]== 1) printf("%d is a prime\n",N);
  }
}

Here is my checkprime.c

#include "defs.h"
#include "externs.h"


int CheckPrime(int K)
{

  int J;


  J = 2;

  while (1)  
  {
    if (Prime[J] == 1)
    {
      if (K % J == 0)  
      {
         Prime[K] = 0;
         return 0;
      }
      J++; 
    } 
    break;
  }   

  Prime[K] = 1; 
}

Upvotes: 1

Views: 48

Answers (1)

Tom Karzes
Tom Karzes

Reputation: 24052

There are some problems in CheckPrime with the loop exit conditions. Use the following instead:

int CheckPrime(int K)
{
    int J;

    for (J=2; J*J <= K; J++) {
        if (Prime[J] == 1) {
            if (K % J == 0) {
                Prime[K] = 0;
                return 0;
            }
        }
    }

    Prime[K] = 1;
    return 1;
}

The rest of it should work with this change.

Upvotes: 1

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