Why is my code returning 0.00?

Question

#include <stdio.h>
#include <math.h>

float math(int, int, int, int, int, float, float, float);

main() {
  int a, b, c, d, e;
  float sum, avg, sd;
  printf("Enter Five Integers->");
  scanf("%d%d%d%d%d", &a, &b, &c, &d, &e);
  math(a, b, c, d, e, sum, avg, sd);
  printf("Sum=%.2f\nAverage=%.2f\nStandard Deviation=%.2f", sum, avg, sd);
}

float math(int a, int b, int c, int d, int e, float sum, float avg, float sd) {
  sum = a + b + c + d + e;
  avg = (sum) / 5;
  sd = pow(
      ((pow(a - avg, 2) + pow(b - avg, 2) + pow(c - avg, 2) + pow(d - avg, 2),
        pow(e - avg, 2)) /
       5),
      0.5);
  return sum, avg, sd;
}

My program always returns the answer 0.00. Can anyone explain what is the problem with my code?

Please indent your code properly. Read what the comma operator does, you're not assigning return value; variables are passed by value, thus changing them in a function doesn't help at all etc. — Antti Haapala -- Слава Україні, Feb 26 '17 at 07:18
What does the debugger tell you when you step through the code? — Ken White, Feb 26 '17 at 07:19
Your `math` function doesn't return what you think it does (read about [the comma operator](http://en.cppreference.com/w/c/language/operator_other#Comma_operator)). You probably need to [find a good beginners book](http://stackoverflow.com/questions/562303/the-definitive-c-book-guide-and-list) and read a little more about functions and how arguments and return values work. — Some programmer dude, Feb 26 '17 at 07:19
Thank you for your help. My code is supposed to "return" the sum,average and standar deviation of the five integers entered. — Muneeb Ahmed, Feb 26 '17 at 07:59

Sourav Ghosh · Answer 1 · 2017-02-26T07:30:43.857

TL;DR Because, your code invokes undefined behavior and no justification can be made to reasonify the output.

To elaborate, first thing, the statement

 return sum, avg, sd;

does not do what you think it's doing. It does not return three values together, rather due to the usage of comma operator, it returns only sd.

That said, you did not collect the return value of the function call anywhere in your code, so there's no way you are going to get any valid output returned from the function call in the caller, there.

After that, you end up using

 printf("Sum=%.2f\nAverage=%.2f\nStandard Deviation=%.2f", sum, avg, sd);

where, the supplied variables (automatic, local variables) remains uninitialized, essentially trying to make use of indeterminate values which invokes undefined behavior.

Finally, for a hosted environment, the conforming signature for main() should be int main(void), at least.

Solution: You need to either

Pass pointers to those variable in which you want to store the results from the called function and then, in the caller you can use them to retrieve the updated value.
Form a structure containing all the variables for which you want the computed value to be returned, populate and return the structure. Then, in the caller, collect the returned value in another structure type variable and then, use individual member elements to print the value.

Thank you for your help. I have just started programming a few days ago and i have not studied pointers yet, so i do not know how to use them. — Muneeb Ahmed, Feb 26 '17 at 07:56
I will try to rewrite this code using pointers in a few days. Thank you for you help! — Muneeb Ahmed, Feb 26 '17 at 08:12

score 0 · Answer 2 · answered Feb 26 '17 at 16:31

There are few taking points in your code.

In C you can't return more than 1 value from a function. You are trying to return 3 vales, as these are separated using "comma(,)", only last value is returned.
There is a difference between local variables of two functions. You can't assign them in 1 function and use it in other without proper reference.
You made function as "call by value" (read more about it in link). As you desire changed values, you should use "call by refernce", which uses pointers.

So the easiest fix for you will be using global variables.

void math(int, int, int, int, int);     //Changed function declareation
 double sum,avg,sd; //New global variables

 int main()
 {
    int a, b, c, d, e;
    printf("Enter Five Integers->");
    scanf("%d%d%d%d%d", &a, &b, &c, &d, &e);
    math(a, b, c, d, e);        //Changed function calling
    printf("Sum=%.2f\nAverage=%.2f\nStandard Deviation=%.2f\n", sum, avg, sd);
    return 0;
}

 void math(int a, int b, int c, int d, int e)
 {
    sum = a + b + c + d + e;
    avg = (sum) / 5;
    double result = (pow(a - avg, 2) + pow(b - avg, 2) + pow(c - avg, 2) +  pow(d - avg, 2) + pow(e - avg, 2) ) / 5;
    sd = pow(result , 0.5);
 }

Using global variables is not a good way of solving the problem. It works; it may even be fairly easy; it is not good practice, though. There are other problems with the scenario too (not of your making — of the original scenario). In particular, passing a fixed number of value is odd. A better solution would read a semi-arbitrary number of values into an array, and the code in the function would process the array. — Jonathan Leffler, Feb 26 '17 at 17:41

Why is my code returning 0.00?

2 Answers2