Thread: Validating an Integer

Dear all,

I am a total beginner to C - I've got some code that I'm trying to write that ensures you're entering an integer between 1 and 1000 inclusive. I want to verify the integer is the correct length (4), and that it is an integer.

Code:

void enterN(int *inputInteger)
{
  char str[5] = { };
  int isValid = 0;
  while (isValid == 0) {
    scanf("%5s", str);
    if (strlen(str) > 4) {
      printf("Please enter a number within 1-1000: ");
      char c = 0;
      while ((c = getchar()) != '\n' && c != EOF);

    }

    char *endptr = NULL;
    *inputInteger = strtol(str, &endptr, 10);
    errno = 0;

    if (str == endptr) {
      printf("Not an integer.");
    }

    if (errno != 0) {
      printf("Not an integer, errored.\n");
    }

    if ((strtol(str, &endptr, 10) >= 1) && (strtol(str, &endptr, 10) <= 1000)) {
      isValid = 1;
    }

    else {
      printf("Something wrong with input");
      printf("%s", str);
    }
  }
  printf("%s", str);
}

Every time I test my program by typing values such as 11111, it throws up the else condition saying something is wrong, immediately after saying values are too long. I don't want two errors - I have a feeling I'm not flushing a buffer properly but I have no idea how to do this and what to change.

Values like 111, and 1000 work.

Could someone please help me edit my code to fix this? Thank you!

> char str[5]
You need to make this larger, if you want to allow invalid input and have a chance to validate it.

> scanf("%5s", str);
Or more specifically, the number here needs to be one less than the size of your array.