/* append.c:    Append a formatted string to another string */

#include <stdio.h>
#include <string.h>
#include <stdarg.h>

char *append(char *s, char *fmt, ...)
{
    if (s && fmt)
    {
        va_list args;
        va_start(args,fmt);
        vsprintf(s+strlen(s),fmt,args);
        va_end(args);
    }
    return s;
}

main()
{
    char s[81] = "We're";
    append(s," number %d!\n",1);
    puts(s);
    return 0;
}

Output:
We're number 1!
