How can I find out if the entered digit symbol is?

IsDigit function does not work:

# include & lt; stdio.h & gt;
#Include & lt; stdlib.h & gt;
#Include & lt; Time.h & gt;
#Include & lt; unistd.h & gt;
#Include & lt; ctype.h & gt;
Int Main (Int Argc, Char Const * ArgV []) {
  SRAND (TIME (NULL));
  int score = 0;
  While (1) {
    int x = atoi (argv [1]) + rand ()% ATOI (argv [2]);
    int y = atoi (argv [1]) + radand ()% ATOI (argv [2]);
    int OperationSignNumber = 1 + Rand ()% 2;
    INT RESULT = 0;
    Switch (OperationSignNumber) {
      Case 1:
        Printf ("+ ------------------ + \ n");
        PrintF ("% i +% i =? \ n", x, y);
        PrintF ("+ ------------------ + \ n");
        result = x + y;
        Break;
      Case 2:
        PrintF ("+ ------------------ + \ n");
        PrintF ("% i -% i =? \ n", x, y);
        Printf ("+ ------------------ + \ n");
        result = x - y;
        Break;
    }
    int userswer = 0;
    int answerwasgiven = 0;
    PrintF ("\ N & GT;");
    Scanf ("% I", & amp; UseRSWER);
    if (! IsDigit (UseRSwer)) Break; // & lt; & lt; ----
    System ("Clear");
    if (useranswer == result) {
      Printf ("+ ------------------ + \ n");
      PrintF ("| Right! | \ n");
      Printf ("+ ------------------ + \ n");
      SCORE ++;
    } else {
      Printf ("+ ------------------ + \ n");
      PrintF ("| Left! | \ n");
      PrintF ("+ ------------------ + \ n");
    }
    SLEEP (1);
    INT TIMER = 3;
    While (Timer) {
      System ("Clear");
      PrintF ("+ ------------------ + \ n");
      PrintF ("| Get Ready!% i ... | \ n", Timer);
      PrintF ("+ ------------------ + \ n");
      Timer--;
      SLEEP (1);
    }
    System ("Clear");
  }
  System ("Clear");
  Printf ("+ ------------------ + \ n");
  Printf ("You Score:% i ... \ n", score);
  PrintF ("+ ------------------ + \ n");
  Return 0;
}

I start the program: ./ Quick_math 1 3 . Displays 1 + 1 . I enter 2 and the program closes. I tried to compile using Clang 3.6 and GCC-4.8.4 – the result is the same.

Answer 1, Authority 100%

The function isDigit defines whether the younger byte of an integer number is the int specified as an argument, the character code of the number. That is, she does not what you assume.

You just should replace these two proposals

scanf ("% i", & amp; useranswer);
if (! IsDigit (UseRSwer)) Break;

One offer:

if (scanf ("% i", & amp; userswer)! = 1) Break;