char array size question, please help!

Anyone happen to know why this is? Thanks, Ash

Code:

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/* Anytime you want to use input validation, always make the char array 2 bigger than what you need or it won't work.I'm
not sure why this is because it seems like the program below would work, but it you don't change str[6] to str[7], it
doesn't.
When fgets gets a string it will save 1 spot for the \0, and you'll need a space for the \n as well.
That's why in the program below which wants a 5 digit number, it seems like using "char str[6]" would work fine.
That should mean that fgets will also save str[6] for the \0 and str 0 - 4 would be for the 5 digit number
and str[5] would be for the \n, but this doesn't work, only if you change "char str[6]" to "char str[7]", but why???


*/

#include <stdio.h>

int main() {

int lp;
int cb;
char overflow = 'x'; //to make sure it doesn't get assigned something else when defined.
int input;
int nchars;
int returncode;
char str[6];

printf("Enter a 5 digit number:");

fgets(str, sizeof(str), stdin);  //fgets will save str[6] for the \0

if (str[5] != '\n') {
  printf("Not a 5 digit number\n");

  for (lp = 0;lp < sizeof(str); lp++) {
      if (str[lp] == '\n') {
          overflow = 'F';
          }
          }
    if (overflow != 'F') {
      printf("Overflow = T\n");
      while ((cb=getchar()) != '\n');
      }
    main();
  }

  //

for (lp = 0; lp < sizeof(str); lp++) {
    if (str[lp] == '\n') {
      str[lp] = '\0';
                        }
      }



returncode = sscanf(str, "%d%n", &input, &nchars);

if (returncode != 1) main();

if ((returncode == 1) && (str[nchars] != '\0')) main();

else printf("Good job!");

getchar();
exit(0);
}

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str[6] contains
1 2 3 4 \n \0
That's 6 chars in total - but you only typed in 4 actual characters of data.

Also, please learn how to use loops, and not call main() recursively.

Quote:

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Originally Posted by Ash1981

That should mean that fgets will also save str[6] for the \0 and str 0 - 4 would be for the 5 digit number
and str[5] would be for the \n, but this doesn't work, only if you change "char str[6]" to "char str[7]", but why???

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With 'char str[6]' a reference to str[6] is outside of your array. Remember that the numbering is zero-based: in this case 0-5

Code:

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if (returncode != 1) main();

if ((returncode == 1) && (str[nchars] != '\0')) main();

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In C++ it's illegal to call main(). In C you can do it, but you should probably use a loop instead.

thanks all