sprintf

sprintf does a printf into a buffer. It's how you convert
numbers to strings.

sprintf.c

#include <stdio.h>

int main( void ) {
    char formatted_id[25];
    int division   = 90125;
    int unit       = 2112;
    int department = 5150;

    sprintf( formatted_id, "%6d-%04d-%06d", division, unit, department );

    printf( "ID = %s\n", formatted_id );

    return 0;
}

$ sprintf

ID =  90125-2112-005150

It's up to you to make sure the buffer is big enough, and you don't
run past the end.