How to concatenate string and int in C?

Strings are hard work in C.

#include <stdio.h>

int main()
{
   int i;
   char buf[12];

   for (i = 0; i < 100; i++) {
      snprintf(buf, 12, "pre_%d_suff", i); // puts string into buffer
      printf("%s\n", buf); // outputs so you can see it
   }
}

The 12 is enough bytes to store the text "pre_", the text "_suff", a string of up to two characters ("99") and the NULL terminator that goes on the end of C string buffers.

This will tell you how to use snprintf, but I suggest a good C book!

Use sprintf (or snprintf if like me you can't count) with format string "pre_%d_suff".

For what it's worth, with itoa/strcat you could do:

char dst[12] = "pre_";
itoa(i, dst+4, 10);
strcat(dst, "_suff");

Look at snprintf or, if GNU extensions are OK, asprintf (which will allocate memory for you).