Averaging 3 integers

Question

My assignment is to fix the code. I have my edited code below and the original code below that. I figure I still have a few errors in here. My error checking doesnt seem to work, and I am not sure if my getchar() function is written or working properly.

Please assume I know nothing becasue that is fairly accurate.

The code compiles, but the answer is always 2. I am about 4 hours into this piece of code with 3 more to work after this.

My code

#include <stdio.h> 

double get_number(double num);

main () {
  double n1,n2,n3;
  double average;

  printf("\nCompute the average of 3 integers\n");
  printf("--------------------------------\n");
  n1 = get_number(1);
  n2 = get_number(2);
  n3 = get_number(3);
  average = (n1 + n2 + n3)/3;
  printf("The average is %0.2f\n",average);
}

double get_number(double num) { 
  double value = 0;
  char c;
  int i;
  printf("Please input number %d: ", num);

  while (c = getchar != '\n') { 
    if ( (c>9) || (c<0) ) { 
      printf("Incorrect character entered as a number - %c\n",c);
      return(0);
    }
    else {
    value = num;
    }
  }
  return(value);
}

Original code

#include <stdio.h> 

main () {
  double n1,n2,n3;
  double average;

  printf("\nCompute the average of 3 integers\n");
  printf("--------------------------------\n");
  n1 = get_number(1);
  n2 = get_number(2);
  n3 = get_number(3);
  average = (n1 + n2 + n3)/3;
  printf("The average is %0.2f\n",average);
}

double get_number(int num) { 
  double value = 0;
  char c;
  printf("Please input number %d: ", num);
  while (c = getchar() != '\n') { 
    if ( (c<=9) && (c>=0) ) { 
      printf("Incorrect character entered as a number - %c\n",c);
      exit(-1);
    }
    else {
      value = 10*value + c - '0';
    }
  }
  return(value);
}

Answer 1

A few issues:

1. You should be using '9' and '0', since you want the ASCII values for digit '9' (0x39) and '0' (0x30), not 0x9 and 0x0.

if ( (c>'9') || (c<'0') ) { 

2. != has higher precedence than =, so you need parens. Learn operator precedence, and if you're in doubt, use parens:

3. getchar is a function not a variable.

while ((c = getchar()) != '\n') { 

4.  You use the wrong conversion. num is a double, so you would need %f. Or, you could make num a int.

printf("Please input number %f: ", num);

5. You never actually use c in any way (except error checking). You always return 0 or num (see your else clause), which makes no sense. The else body of the original is correct.

Answer 2

You got the floating point parsing all wrong and shouldn't be doing it yourself. There's an easier way:

double get_number(double num) { 
  double value = 0.0;
  printf("Please input number %lf: ", num);
  scanf("%lf", &value);
  return(value);
}

Answer 3

The issues with the original program are:

1. getchar() returns an ASCII code, and the condition was wrong. When checking for boundaries, use ((c<'0') || (c>'9')).
2. For the exit function you need to include "stdlib.h".
3. For the main function to understand what is get_number, you need to either move the function to be before the main function, or you can use a forward declaration.
4. The assignment operator (=) has lower precedence than the inequality operator (!=), so you need to use parenthesis, like: ((c = getchar()) != '\n')

You have actually created several more issues, so I wouldn't rely on your code.

In any case, in general - it is advised you study how to use a debugger. Once your code is compiling (and for that you'll need to get accustomed to the compilation error messages), you need to start debugging your code. I suggest you take some time to learn how to set breakpoints, set watches, and go step by step into your code. That skill is absolutely essential for a good developer.

Answer 4

Here's how I'd go about correcting the code ...

1. http://ideone.com/a0UMm -- compilation errors
2. http://ideone.com/ljUg1 -- warnings, but it works now
3. http://ideone.com/Qd0gp -- no errors, no warnings, test run ok

For 1. I used the "original code" as posted by you.

For 2. I used int main(void), declared the function get_number before defining main, added parenthesis in line 20, and added #include <stdlib.h>

For 3. I added return 0; before the final } of main. I also removed the extra output that messed up the ideone interface (it looks better on an interactive interface)

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Edit more tests needed to complete the task of correcting the original code