strcat:concatenate t to end of s.

/*strcat: concatenate t to end of s; s must be big enough */
void strcat(char s[], char t[])
{
   int i, j;

   i = j = 0;
   while(s[i] != '\0')            /*find end of s*/
         i++;
   while ((s[i++] = t[j++]) != '\0')   /* copy t */
           ;
}