Function returning memory address

Question

I'm trying to write a program that will read in the number of values for an array, call a function to input said values and then compute the average. From there it will call another function to print off a corresponding message. The problem is that it appears to be returning what would be a memory address.

Thanks in advance!

Here is my code:

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

int compute_grade_avg(int grades[], int size)
{

  int i, result, average, sum=0;

  //Ask the user for the specific grades                                                                                           
  for(i=0;i<size;i++){
    printf("Enter a grade:\n");
    scanf("%d", &grades[i]);
  }

  //Calculate the sum of values in the array                                                                                       
  for(i=0;i<size;i++){
    sum += grades[i];
  }

  //Calculate the average based off of the sum and size of the array                                                               
  average = sum/size;
  result = ceil(average);

  return result;
}
//Function to print the corresponding message                                                                                      
int write_grade_message()

{
  int average;

  //Messages to print depending on grade                                                                                           
  if (average < 60){
    printf("Failed semester - registration suspended");
  }
  else if(average < 69){
    printf("On probation for next semester");
  }
  else if(average < 79){
    printf("");
  }
  else if(average < 89){
    printf("Dean's list for the semester");
  }
  else if(average < 100){
    printf("Highest honors for the semester");
  }
  return(0);
}
//Main Function                                                                                                                    
int main()
{
  int size, average;

  //Enter the number of grades that will go into the array                                                                        \

  printf("Enter the number of grades to be entered:\n");
  scanf("%d", &size);

  int grades[size];


  //Call compute grade average function                                                                                            
  average = compute_grade_avg(grades, size);

  //Call write grade message function                                                                                              
  write_grade_message(average);

  return(0);
}

Answer 1

• First, If you execute the original code with warnings it will say

  warning: 'average' is used uninitialized in this function [-Wuninitialized],

this is because at no time of the function the user is asked the average value. Looking at the code a little, we see that the variable average is calculated as average = compute_grade_avg (grades, size);. Consequently, what must be done is to pass to function write_grade_message the variable average. It would be like this int write_grade_message (int average). Second, "" would be an empty string, but an empty string is not defined like this in C, but it occurs to me to put a space "" between the two quotes. Third, the comment Enter the number of grades that will go into the array should be commented / * * / and not //. The whole program would be like that:

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

int compute_grade_avg(int grades[], int size)
{

    int i, result, average, sum=0;

    //Ask the user for the specific grades                                                                                           
    for(i=0;i<size;i++){
        printf("Enter a grade:\n");
        scanf("%d", &grades[i]);
    }

    //Calculate the sum of values in the array                                                                                       
    for(i=0;i<size;i++){
        sum += grades[i];
    }

    //Calculate the average based off of the sum and size of the array                                                               
    average = sum/size;
    result = ceil(average);

    return result;
}
//Function to print the corresponding message                                                                                      
int write_grade_message(int average)

{
    //int average=0;

    //Messages to print depending on grade                                                                                           
    if (average < 60){
        printf("Failed semester - registration suspended");
    }
    else if(average < 69){
        printf("On probation for next semester");
    }
    else if(average < 79){
        printf(" ");
    }
    else if(average < 89){
        printf("Dean's list for the semester");
    }
    else if(average < 100){
        printf("Highest honors for the semester");
    }
    return(0);
}
//Main Function                                                                                                                    
int main()
{
    int size, average;

    /*Enter the number of grades that will go into the array */                                                                       \

    printf("Enter the number of grades to be entered:\n");
    scanf("%d", &size);

    int grades[size];


    //Call compute grade average function                                                                                            
    average = compute_grade_avg(grades, size);

    //Call write grade message function                                                                                              
    write_grade_message(average);

    return(0);
}

Answer 2

The call of write_grade_message(average); is passing a parameter average. However, the function has no parameter, instead a declaration of a local variable average which is not initialized.

the function should be update like this.

int write_grade_message(int average)
{
// int average; ======> then removed this line

Answer 3

The problem is specifically that you passed a paramter to int write_grade_message() that takes an unspecified number of parameters, which makes the code compile but has as it is now undefined behavior.

There is yet another source for undefined behavior to happen, because you redeclared average inside write_grade_message() and you tried to read the value without previously initializing it¹. You need to change write_grade_message() to read

void write_grade_message(int average) ...

and remove the internal declaration of average and your code will probably work just fine, also read the comments to your question for more useful tips.

If your code compiled cleanly and without issuing any warnings or messages, then you need to enable your compiler's warnings and diagnostics, which not only help you see through some silly mistakes that you can make sometimes, but also should help you learn the language deeply, since you can infer from the warning messages some useful knowledge about the language.

---

¹_{In C, not initializing a variable explicitly — except for global variables, or variables with the static storage class — would leave the variable uninitialized. Any attempt to use it other than initialize it, would invoke what is called undefined behavior}

Answer 4

Your problem is that int write_grade_message(); is a function that can take any number of parameters but you won't see them inside write_grade_message.

You have to declare it like this:

int write_grade_message(int average)
{
    // your code
    if (average < 60){
        printf("Failed semester - registration suspended");
    }
    else if(average < 69){
        printf("On probation for next semester");
    }
    else if(average < 79){
        printf("");
    }
    else if(average < 89){
        printf("Dean's list for the semester");
    }
    else if(average < 100){
        printf("Highest honors for the semester");
    }

    return(0);
}

Also note that in compute_grade_avg the variables average, sum and size are of type int. Division with ints returns you always an int, so ceil won't round up the number. You would need to use floating points for that. However you have to change the type of the function to return float and result and average must be floats too.

float compute_grade_avg(int grades[], int size)
{
    float result, average;

    ...

    average = ((float) sum)/size;
    result = ceil(average);

    return result;
}