Average of an Array

[Peteski]

I am writing a program to calculate the average of an array of 10 floating-point values. I am trying to write it so that the value entered by the user goes straight to the array.

My problem is that the program isn't adding up the values in the array.

// Program to calculate the average of an array of 10 floating-point values


#include <stdio.h>


int main (void)
{
    float grades[10], average;
    int i, gradeTotal = 0;


    for ( i = 1; i <= 10; ++i ) {
        printf ("Enter 10 values to be averaged #%i: ", i);
        scanf ("%i", &grades[i]);


        gradeTotal = gradeTotal + grades[i];
    }


    average = (float) gradeTotal / 10;


    printf ("\nGrade average = %.2f\n", average);


    return 0;
}

[memcpy]

gradetotal should be a float, and i should start at 0.

Also, I would try avoid scanf and use fgets() and atof() to convert to a float.

[Peteski]

gradetotal should be a float, and i should start at 0.

Also, I would try avoid scanf and use fgets() and atof() to convert to a float.

Changing i to 0 starts the numbering in the printf at 0, instead of 1.

I changed gradeTotal to a float and instead of getting the last entry in the array, now I get 0.00.

I have seen people say to avoid scanf several times. Why is that? I haven't learned how to use anything else yet.

[whiteflags]

In addition to memcpy's comments, the 10th array element doesn't exist (since you start from zero the largest you can go is size - 1).

scanf ("%i", &grades[i]);
%i doesn't convert input to a float, it converts input to a signed integer like %d does.

[Amberlampz]

float grades[10]

You're telling the system to create an array of 10 floats containing indexes 0 through 9.

for ( i = 1; i <= 10; ++i )

And you're now telling the system to iterate from the 1st to the 10th index, which doesn't exist (problem).

scanf ("%i", &grades[i]);

There's nothing wrong with using scanf(), but you need to match types properly.

average = (float) gradeTotal / 10;

You could also just put that calculation in your printf() statement. It's not any faster as far as the system is concerned, just another way to do things.

[whiteflags]

You could also just put that calculation in your printf() statement. It's not any faster as far as the system is concerned, just another way to do things.

Well, then why do it? I mean, do a calculation once, and store the answer in a variable, then you have that. Do it inline, and you have to calculate it every time.

[iMalc]

Once you fix the bounds of your for loop, you can make a simple change to your printf:

        printf ("Enter 10 values to be averaged #%i: ", i+1);

(notice the +1)

[Peteski]

Thank you all for your help, but I am still getting 0.00 after I enter the 10 values. Below is my updated code. Maybe I missed something one of you said.

// Program to calculate the average of an array of 10 floating-point values


#include <stdio.h>


int main (void)
{
    float grades[10], average, gradeTotal = 0;
    int i;


    for ( i = 0; i <= 9; ++i ) {
        printf ("Enter 10 values to be averaged #%i: ", i+1);
        scanf ("%i", &grades[i]);


        gradeTotal = gradeTotal + grades[i];
    }


    average = gradeTotal / 10;


    printf ("\nGrade average = %.2f\n", average);


    return 0;
}

[failure67]

Look at line 15.

[Peteski]

Look at line 15.

I tried using fgets, although I admit that I may be using it wrong. With fgets, it says that the array needs to be char, instead of a float.

[stahta01]

scanf - C++ Reference

What does the format specifier "i" mean?

Note: I wish you to read the data I linked!

Tim S.

[Peteski]

scanf - C++ Reference

What does the format specifier "i" mean?

Note: I wish you to read the data I linked!

Tim S.

Thanks for the reference! I have tried changing the %i in scanf to %f, but I didn't see any changes. The average is still 0.00.

[stahta01]

Enter 10 values to be averaged #1: 1
Enter 10 values to be averaged #2: 2
Enter 10 values to be averaged #3: 3
Enter 10 values to be averaged #4: 4
Enter 10 values to be averaged #5: 5
Enter 10 values to be averaged #6: 6
Enter 10 values to be averaged #7: 7
Enter 10 values to be averaged #8: 8
Enter 10 values to be averaged #9: 9
Enter 10 values to be averaged #10: 10

Grade average = 5.50

Works for me.
You do realize the total should be of type float to work with some inputs?

Tim S.

[grumpy]

The end condition would be "i < 10", not "i <= 9". What you have is not technically wrong, but increases chances of self-imposed confusion.

After making the change, ensure you actually recompile and relink as appropriate. Depending on input you supply, average can also be zero.

[iMalc]

%i is fine for printing out and integer in the printf, but it is not the right thing for scanf to read in a float.

Edit: Wow, I had this page loaded for far too long before I replied.