Segmentation fault while using strcat(num, num) to concatenate string to itself

Question

I used strcat function to concatenate "1" and "1" so that the result is "11" but I'm getting a segmentation fault.

My code is below:

#include <stdio.h>
#include <string.h>
int main(){
  char num[10] = "1";
  strcat(num, num);
  printf("%s", num);
}

Answer 1

You need two char[] one as source and other for destination, where destination array must be initialized and have enough space to accommodate source length.

#define DEST_SIZE 40

int main(){
  char num[10] = "1";
  char dest[DEST_SIZE] = "1"; //Destination with null characters after "1"
  strcat(dest,num);
  printf(dest);
  return 0;
}

For detailed explanation about different scenarios : here