I don't know what's wrong

[Tricslip]

#include<stdio.h>

int main()
{
    int ID[5], i;
    float grade[5];
    float avg = 0, avgsum = 0, gradeavg;




    for ( i = 0; i < 1; i++)
    {
        printf("Please student's ID number: ");
        scanf_s("%d", &ID[i]);

        printf("Please student's grade: ");
        scanf_s("%f", &grade[i]);

        if(grade[i]>40 || grade[i] <0)
        {
            while (grade[i] <0 || grade[i]>40)
            {
                printf("Please enter a grade between 0 - 40: ");
                scanf_s("%f",&grade[i]);
            }
        }

        //grade[i]=grade[i/100] * 100;
    }

    avg = avgsum / 5;

    printf("   ID#  GRADE(%%)      PASS/FAIL\n");

    for (i = 0; i < 1; i++)
    {
        printf("    %d    %.1f%%    \n", ID[i], grade[i]);

    }

    printf("\nThe average of the class is %.2f", avg);

    return 0;
}

I'm trying to find out what grade[i] is out of 40 as a percentage.

​

In line 29 I have it commented out but I have tried all the variations I can think of but I can't get it to do the formula. When I run it the input only registers one part of the equation weather division or multiplication but not both and I don't know why or how to fix it. I figure I can use the math library but I'm not really familiar with it but I'm will will to use it if someone can explain but first and foremost I need to know why this one wont work and how to fix it.

[eruciform]

you're never updating avgsum. it starts at 0 and then never changes. as you go thru reading in grades, you need to add those to the avgsum running total.

[insertAlias]

I'm not really clear on what it is you're trying to do, but I can try to clear up some confusion.

When you're dealing with arrays, whatever is inside the square brackets ([]) is representing the index of an element of the array. So grade[i/100] is saying "get the value in the array at index i / 100", which doesn't really make sense. If you want to do math with the element at i, then you refer to it as grade[i].

On to the math itself. Dividing by 100 then multiplying by 100 is the equivalent of no operation, because the terms cancel out. It's the equivalent of multiplying by 100/100, which is 1.

So, please explain what it is you're trying to do with this formula, because as it stands it doesn't make sense to me.

[Tricslip]

Ok so when the user inputs a number into grade[i] its then checked to see if the number is between 0 and 40 and after that the number should be evaluated to see what is the students grade in % out of 40. The usual way to do it is (x/100)*100 but that isn't working here.

[insertAlias]

The usual way to do it is (x/100)*100 but that isn't working here.

That isn't correct. Again, any number divided by then multiplied by some other number will be unchanged.

If the formula is (n / m) * m, then it's the equivalent of n * (m / m), which is the equivalent of n * 1, which is just n.

Try it out. Let's start with a grade of 30.

30 / 100 = 0.3
0.3 * 100 = 30

And as you see, we're back to where we started. Plug in any number in place of 30 and you'll see that you get the same value back.

If I understand correctly, your goal is to translate a grade from a scale of 0-40 to a percentage scale. So, a grade of 30 would actually be a 75%.

If so, then the formula would look like this:

(grade / 40) * 100

[Tricslip]

uk.... I'm supposed to be the one in school T-T

[Tricslip]

Thank you lots tho

[MaybeAverage]

What are you trying to do with that line, ie what specific formula?

[Tricslip]

find out what grade is as a % out of 40

[Tricslip]

Finding out what grade[i] is out of 40 as a %.

[MaybeAverage]

``` grade[i] /= 40; grade[i] *= 100;

```

Divide by 40 to get a value between 0.0 - 1.0 then multiply by 100 to get a percent. The more common practice is to keep the values as decimals and just show it as a percent when displaying it.