Hi, Was hoping someone could help me out with a slight problem, Im trying to test whether certain strings are valid hex values: here is my code - #include // #include / #include // #include // void checkHexNumber(char *hex) { char *tail; int hexnum; if (strlen(hex) > 2) return 1; else strtol(hex, &tail, 16); } int main() { char *hexNumber = "FF"; checkHexNumber(hexNumber); return 0; } If tail contains letters then strtol has failed, but how can i tell if it passed? I tried if(tail == NULL) which I thought would have worked but it didnt, am i doing something noticeably wrong? I would really appreciate a hand with this. Neil

Neil, A pointer to the first unrecognized character in the string is stored in tail after the call. So to check the result: if (strcmp(tail, "")) // Failed else // Suceeded. Good luck.