c - removing printf statment from code breaks program -

i have problem can't figure out, hope guys can me. wrote c program convert decimal binary , write bits on integer array, works fine until remove couple of printf statements.since thought weird , removing printf statement doesn't change logic of code tried recreate problem on machine , there works 1 expect , without printfs. here code:

#include <stdio.h> #include <stdlib.h>  int main(){  int a; printf("input number:\n"); scanf("%d",&a);  int size=sizeof(a); size=size*8; printf("size in bits: %d\n",size);   int *p; p=malloc(size);   int i; for(i=0;i<size;i++){       p[size-i-1]=a&0x1;      a=a>>1; }  for(i=0;i<size;i++){      printf("%d",p[i]); }  printf("\n");  } 

when remove

printf("input number:\n"); 

and

printf("size in bits: %d\n",size); 

i error

a.out: malloc.c:2392: sysmalloc: assertion `(old_top == initial_top (av)  && old_size == 0) || ((unsigned long) (old_size) >= minsize && prev_inuse (old_top) && ((unsigned long) old_end & (pagesize - 1)) == 0)' failed.aborted (core dumped) 

if helps here output uname -a on machine

linux aaaa 4.4.0-45-generic #66-ubuntu smp wed oct 19 14:12:37 utc 2016 x86_64 x86_64 x86_64 gnu/linux 

and output other machine

linux bernard-inspiron-5558 3.13.0-95-generic #142-ubuntu smp fri aug 12 17:00:09 utc 2016 x86_64 x86_64 x86_64 gnu/linux 

my gcc version

gcc version 5.4.0 20160609 (ubuntu 5.4.0-6ubuntu1~16.04.2)  

and other 1

gcc version 4.8.4 (ubuntu 4.8.4-2ubuntu1~14.04.3) 

does have gcc,the os, or doing wrong in code?

yes, not asking enough memory.

int *p; p=malloc(size); // size in bytes  int i; for(i=0;i<size;i++){     p[size-i-1]=a&0x1;  // size - 1 ints.     a=a>>1; } 

you need malloc enough memory size ints. i.e.

malloc(size * sizeof(int)); 

writing past allocated memory undefined behavior.