C program to print twin prime numbers

C program to print twin prime numbers

Input:

Enter the range to find twin primes below it:
50

Output:

3 & 5 are twin primes
5 & 7 are twin primes
11 & 13 are twin primes
17 & 19 are twin primes
29 & 31 are twin primes
41 & 43 are twin primes

Implementation:

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <math.h> #include <limits.h> #define MAX 1000000 int hash[MAX]={0}; void sethash(int n) { int i; for(i=1;i*n<MAX;i++) { if(hash[i*n]==0) { hash[i*n]=1; } } } int checktwins(int x,int y) { return (abs(x-y)==2); } int main(void) { int n; int i; int curprime=2,nextprime; printf("Enter the range to find twin primes below it:\n"); scanf("%d",&n); for(i=2;i<n;i++) { if(hash[i]==0) { nextprime=i; if(checktwins(curprime,nextprime)) { printf("%d & %d are twin primes\n",curprime,nextprime); } curprime=nextprime; sethash(i); } } return 0; }