#include int main() { //int n = 0; int i, k, prime; int iter = 0; int len = 0; int primePos = 0; long long r, prev; char c; while (iter < 200) { printf("How many numbers to check?\n> "); scanf("%d", &iter); if (iter < 200){ printf("Needs to be at least 200.\n"); } } printf("List prime calculation? (Y/n)\n> ", iter); scanf(" %c", &c); printf("Calculating..."); //printf("Org~~~~Rev"); int primes[iter*sizeof(int)]; int rprimes[iter*sizeof(int)]; //Prime list builder for (i = 1; i < iter; i++) { prime = 1; if (i < 3) { primes[primePos++] = i; if (c == 'Y' || c == 'y') { printf("\n%d", primes[primePos-1]); } continue; } for (k = 2; k < i; k++) { if ((i % k) == 0) { prime = 0; } } if (prime) { primes[primePos++] = i; if (c == 'Y' || c == 'y') { printf("\n%d", primes[primePos-1]); } } } i = 0; //Getting length up to last prime while (len == 0) { if (primes[i] == '\0') { len = i-1; //printf("\n----------------------------------------------------------\nLen is %d\n----------------------------------------------------------", len); } i++; } //Reverser and checker printf("\n\n~~~~~~~~~~~~~~~~~\n"); primePos = 0; for (i = 0; i < (len+1); i++) { prime = 1; r = 0; prev = 0; //printf("\n%d. ", i); if (primes[i] < 10) { continue; } else { r = primes[i]; while (r != 0) { prev *= 10; prev += (r % 10); r /= 10; //printf("\n%d", prev); } //printf("\n%d reversed: %d", primes[i], prev); for (k = 2; k < i; k++) { if ((prev % k) == 0) { prime = 0; } } if (prime) { rprimes[primePos++] = primes[i]; printf("\n%d <-> %d", rprimes[primePos-1], prev); } } } printf("\nPress ENTER key to exit...\n"); getchar(); getchar(); return 0; }

reversiblePrimes