c - Command terminated when inputting large number -

how come message "command terminated" when try input large number (around 10 million)? program displays whether number prime or not.

see code below:

#include <stdlib.h> #include <stdio.h> #include <stdbool.h>  int main ( int argc, char *argv[] ) {    unsigned long long number;    bool prime ( unsigned long long );     printf ("enter positive integer greater 1: ");    scanf ("%llu", &number );     prime( number ) ?       printf ( "%llu prime.\n", number ):       printf ( "%llu not prime.\n", number);     return exit_success; }  bool prime ( unsigned long long number ) {    unsigned long long i, j;    bool isprime[number + 1];     ( = 2; <= number; i++ )       isprime[i] = true;     ( = 2; <= number - 1; i++ )       ( j = 1; i*j <= number; j++ )          isprime[i*j] = false;     return isprime[number]; } 

the problem attempt create array isprime on stack larger available memory. should create on heap instead, using

bool *isprime; isprime = malloc((number + 1) * sizeof *isprime); 

do once obviously, not every call function prime

notice if want know if number prime, need search far square root of number factor - , if find factor done. makes size of array have create more manageable - involve changes algorithm.

afterthought have problem in logic determines prime number - inner loop starts j=1 means prime numbers marked non-prime. following "slightly improved" code - although there's more make better:

#include <stdlib.h> #include <stdio.h> #include <stdbool.h> #include <math.h>  int main ( int argc, char *argv[] ) {    unsigned long long number;    bool prime ( unsigned long long );     printf ("enter positive integer greater 1: ");    scanf ("%llu", &number );     prime( number ) ?       printf ( "%llu prime.\n", number ):       printf ( "%llu not prime.\n", number);     return exit_success; }  bool prime ( unsigned long long number ) {    unsigned long long i, j, sq;    bool *isprime;    sq = ceil(sqrt(number));    isprime = malloc((sq + 1)*sizeof *isprime);     // generate primes square root of number    ( = 2; <= sq; i++ )       isprime[i] = true;     ( = 2; < sq; i++ ) {       // need mark multiples if prime:       if(isprime[i]) {         // start loop @ 2, not 1!         ( j = 2; i*j <= sq; j++ ) {           isprime[i*j] = false;         }       }     }     ( = 1; < sq; i++)    {     if (isprime[i] && number%i==0) return false;    }     return true; } 

basic testing:

gcc -wall generates no errors / warnings

104729 prime (it is); code doesn't crash input of 10000001 (not prime).