Simple C Program

J_K9 · 09-28-2005, 12:51 PM

Dear all,

I am having a problem with a simple C program I have made (I am still very much a beginner), and it would be really kind of you if you could help me trace the error!

Here is the code:

Code:

#include <stdio.h>

/* a program to work out the mean of your exam results */

main()
{
  int total, exams_taken, number, quit;
  printf ("End typing in your results by pressing the \"x\" key\n\n");

  total = 0;
  exams_taken = 0;
  number = 0;
  quit = "x";

  while (number != quit) {
    printf ("%d. Please input your exam result (out of 100):\n", exams_taken + 1);
    scanf ("%d", &number);
    total = total + number;
    exams_taken = exams_taken + 1;
  }
  printf ("Your mean mark was: %d", (total / exams_taken)*100);
}

I have realized that actually the while statement has a serious fault - that when the end character (x) is typed, it will try adding that to the int "Total", which just wouldn't work. Anyway, the - current - problem is different: once the 'x' character is entered, the input disappears but the output of "Please input your exam result (out of 100):" continues on the loop. This shouldn't happen, but I can't see the error I've made....could anyone please help me? Thanks!

M.

jtshaw · 09-28-2005, 01:12 PM

Your problem is scanf with "%d" is never going to except a char.

Your going to want to read in the numbers as strings. You can use strtol to convert the string to a long int for math purposes. You can then use strcmp to compare two strings (like the input string with "x").

J_K9 · 09-28-2005, 01:25 PM

Thanks JT! I've tried putting it together though, and it still seems to fail...

I converted the 'number' int to a string, and I read up on strtol, but my usage of it must be wrong, because I get a compilation error. It tells me that strtol wants "const signed char *", which I'm pretty sure has something to do with pointers. Also, 'number' would need to be a variable, not a constant, for the program to work... Am I trying to run before I can walk? Anyhoo, could you please lead me step by step through the while statement? I'd really like to see how I could get this program up and running...

Thanks again!

M.

jtshaw · 09-28-2005, 04:15 PM

Code:

#include <stdio.h>
#include <stdlib.h>

/* a program to work out the mean of your exam results */

int main()
{
        int total, exams_taken, number, quit;
        char *tempstr = malloc(sizeof(char) * 10);
        printf ("End typing in your results by pressing the \"x\" key\n\n");

        total = 0;
        exams_taken = 0;
        number = 0;
        quit = 0;

        while (!quit) {
                printf ("%d. Please input your exam result (out of 100):\n", exams_taken + 1);
                scanf ("%10s", tempstr);
                if (tempstr[0] == 'x') {
                        quit = 1;
                } else {
                        number = strtol(tempstr,NULL,10);
                        total = total + number;
                        exams_taken = exams_taken + 1;
                }
        }
        if (exams_taken > 0) {
                printf ("Your mean mark was: %d", (total / exams_taken));
        } else {
                printf ("There were no scores\n");
        }
        free(tempstr);
        return 0;
}

Ok, I didn't test this very extensively, and it is by no means bullet proof.

First off, I changed the meaning of quit. Consider it a boolean, if it is 0 we aren't going to quit, if it is 1 we will.

The read statement reads in at most a 10 character string (should be plenty big enough). If the first element of the string equals the character 'x' we set quit to 1 and that causes us to quit the loop. If it isn't, we convert it to a number with strtol an go back through the loop again.

After the loop exits, there is a check to make sure some scores were entered (don't want to divide by 0) and if so we do the final calculation and display it.

J_K9 · 09-29-2005, 02:30 AM

Thank you so much, jtshaw!

That was really helpful!!

M.