Get rid off negative averages

So I pulled this from the C++ tutorial here and played around with it to make it into a program that averages ten grades. How ever when I input all negative grades it gives a negative average. How would I and where would I input an if statement(not sure if this is what I would use) that would say basically if the average is less than zero than display ---%.

Thanks for your help I'm pretty new at all of this.

Code:

---

int main()
{
  int grade[10];
  int i,sum=0, avg=0;
  int max=0,min=100;

  for(i=0;i<10;i++)
  {
      cout << "Grade " << i+1 << ": ";
      cin >> grade[i];
  }
  for(i=0;i<10;i++)

  {

      sum=sum+grade[i];

      if(grade[i]>max)

      {

        max=grade[i];

      }

      if(grade[i]<min)

      {

        min=grade[i];

      }

  }

  avg=sum/10;
 

  cout << "Average Grade: " << avg << "%" << endl;

  return 0;
}

---

Example.

Code:

---

if(avg < 0){
}
else{
}

---

Code:

---

cout << "Average Grade: ";
if (avg<0)cout << "---";
else cout << avg;
cout << "%" << endl;

---

would I do something like this?

Minus that being a bit ugly the concept is good.

Code:

---

cout<<"Average Grade: ";
if(avg < 0){
    cout<<"---";
}//if
else{
    cout<<avg;
}//else

cout<<"%"<<endl;

---

Ok great I'll edit that, I also have another question if I still have your attention. How would I split this program up into functions? I tried this but when I enter all my grades I always get 0. Did I split them up right?

Code:

---

int getGrades()

{
      int grade[10];
      int i,sum=0, avg=0;
      int max=0,min=100;

      for(i=0;i<10;i++)
      {
        cout << "Grade " << i+1 << ": ";
        cin >> grade[i];
      }
      for(i=0;i<10;i++)

      {

        sum=sum+grade[i];

        if(grade[i]>max)

        {

            max=grade[i];

        }

        if(grade[i]<min)

        {

            min=grade[i];

        }

      }
}

int averageGrades()
{

  avg=sum/10;

  cout << "Average Grade: ";
  if (avg<0)
      cout << "---";
  else
      cout << avg;
 
  cout << "%" << endl;
}

int main()
{
  getGrades();
  averageGrades();

  return 0;
}

---

I'm surprised that compiles. The concept you are missing is that variables declared in one function do not exist in another function, even if you use the same names. If you declare two variables with the same name in two separate functions, they will reside in two separate memory locations; i.e., they will not be the same variable.

You have to either 1) use global variables (which is generally frowned upon) or 2) learn to pass relevant data between your functions.

I thought I copied the latest of what I had but I declared the variables in both functions thus thats why I was getting zeros, so how do I pass variables then? It goes in the () right?

Read some documentation on it. It will explain things more thoroughly than I will right now (a little busy). Something like:
Cprogramming.com Tutorial: Functions

And I'm sure you can use Google to find other literature on function use. If you have questions after that, feel free to ask.

The average of a bunch of negative numbers is a negative number. What's the problem?

If you want to report that something is wrong, report that the individual grades are negative, not that the overall average is negative.

You know I was thinking about that, how would I do that though? In other words how would I make the program not take into account the value of -1?

And I will read up on it thanks!

Check the value before you process it; if it's negative, skip it, or do whatever kind of error processing you would like.

Since you are using for loops, it might be a good chance to look into the 'continue' keyword and try using that.

So from what I read about passing variables it needs to be in the () of the function that I am passing it too. So in my program would it be

Code:

---

averageGrades(int grade[], int i)

---

edit: Actually I need to pass the avg and the sum right?
Grade is an array so do I include the brackets?

also when I do this I get an "arguement too few compiler" error so that must not be right

so when I pass grade, avg, sum I get a compile error saying expected primary expression before int

When calling a function, you put the names of the variables you want to pass inside the (). Don't include type or other stuff.

I don't declare the type? As in the "int" are you sure? When I do this it just gives me a not declared compiler error. Then when I delcare it in the actual function and in main it still gives me the not delcared in this cope error.

Declaration:

Code:

---

int AverageGrades(int grade[], int i);

---

Calling:

Code:

---

AverageGrades(grade, i);

---

This is what I have now and I still get the undeclared in main. When I declare them then I get another totally different error.

also would it be(something along the lines of this)

Code:

---

if (grade[i] > 100 || grade[i] < 0)
            cout << "---"

---

To get the program to not take into account negative grades in the average?

Code:

---

int getGrades()
{
      int grade[10];
      int i,sum=0, avg=0;
      int max=0,min=100;

      for(i=0;i<10;i++)
      {
        cout << "Grade " << i+1 << ": ";
        cin >> grade[i];
      }
      for(i=0;i<10;i++)

      {

        sum=sum+grade[i];

        if(grade[i]>max)

        {

            max=grade[i];

        }

        if(grade[i]<min)

        {

            min=grade[i];

        }

      }
}

int averageGrades(int grade[], int i)
{
  int avg;
  int sum;

  avg=sum/10;

  cout << "Average Grade: ";
  if (avg<0)
      cout << "---";
  else
      cout << avg;

  cout << "%" << endl;
}


int main()
{

  getGrades();
  averageGrades(grade, i);

  return 0;
}

---

grade and i doesn't exist in main (obviously). They're declared in getGrades. Think about that for a while.
Also, are you coming from C or something? You obviously seem to love declaring variables at top. In C++, this is not necessary.
For example,

Code:

---

for(i=0;i<10;i++)

---

Can be written as:

Code:

---

for(int i = 0; i < 10; i++)

---

Also note how AverageGrade doesn't care about "i". What's it for?

Quote:

---

Originally Posted by Elysia

Also, are you coming from C or something? You obviously seem to love declaring variables at top. In C++, this is not necessary.
...
Also note how AverageGrade doesn't care about "i". What's it for?

---

That's the least of his problems. In fact it's barely even a problem.

Why does GetGrades sum the series of grades, and why does it find the minimum and maximum? It seems like this function can't do one thing well, which is bad. If he is from a C background, he didn't stay long.

Try implementing functions that do one thing:

void GetGrades (int grades[] , size_t size);
double GetAverage (int grades[] , size_t size);
void FindMinMax (int grades[] , size_t size , size_t *minPos , size_t *maxPos);
.. etc ....

If in GetGrades you ensure there are no negative marks, then there wont be negative averages. A good procedural design can isolate all sorts of bugs.

I have no background at all in anything hence why I pulled this from the tutorial here and tried to modify it haha. I have been trying to fool around with this language for about 3 weeks now and not getting too far hah. Sorry for the dumb thought process I just really haven't much of a clue what I'm doing still as you can tell by now. Each thing you post really helps though so thank you and please keep it coming haha.

So I still don't have a clue I've switched the variables all the ways I can think of and it still won't compile, can I get a major hint? maybe in the most simple form possible :)

What is your current code, and how does this updated code not work?

You can see functions are individuals performing work. They have to give them the information they need to carry out the task. And they have to hand that back when they're finished.
You can't just expect individual B to know whatever information individual A carries. And information being variables in this case.

So from getGrades the variables int grade and int sum need to be passed into averageGrades right? Then when I call it in main I just put grade, sum in the () of averageGrades.

edit: it would just be sum because averageGrades doesn't need grade.

this is what I have now, now I get an arguments too many compile error.

Code:

---

int getGrades()
{
      int grade[10];
      int i,sum=0, avg=0;
      int max=0,min=100;

      for(i=0;i<10;i++)
      {
        cout << "Grade " << i+1 << ": ";
        cin >> grade[i];
      }
      for(i=0;i<10;i++)

      {

        sum=sum+grade[i];

        if(grade[i]>max)

        {

            max=grade[i];

        }

        if(grade[i]<min)

        {

            min=grade[i];

        }

      }
}

int averageGrades(int sum)
{

  int avg;

  avg=sum/10;

  cout << "Average Grade: ";
  if (avg<0)
      cout << "---";
  else
      cout << avg;

  cout << "%" << endl;
}


int main()
{
  int sum;

  getGrades(sum);
  averageGrades();

  return 0;
}

---

But GetGrades doesn't take any arguments. You haven't told the compiler that it does.
Also, you seem to not be fully understanding C++ syntax. You might want to read up on functions.

Quote:

---

Originally Posted by Barkley

So from getGrades the variables int grade and int sum need to be passed into averageGrades right? Then when I call it in main I just put grade, sum in the () of averageGrades.

---

Well that's not good enough, obv. Problem is I don't think you understand exactly how a computer executes a program, so I will explain in simple terms with respect to C .

When the computer starts a program it calls main first. Programming folk call main the entry point because that is where the program starts. Now think of main as a task master. The job of main is going to be interact with the user and provide the output he wants. The programmer explains what he wants through writing a series of instructions to be followed in top down order, for the most part. When you have a working program you will have functions that do separate things --

Code:

---

void GetGrades (int grades[] , size_t size);
double GetAverage (int grades[] , size_t size);
void FindMinMax (int grades[] , size_t size , size_t *minPos , size_t *maxPos);

---

main calls these helper functions to do its job. In this program, main might have an average variable to present to the user, which is actually a reduction of the grades array.

The first helper main will have to hand control over to is here at GetGrades. GetGrades promises that grades will be filled when its done. main is a pretty lazy function, and doesn't want to do this itself, so this promise makes everything pretty copacetic. main gives its helper a pointer to grade's first element and a size variable, and then GetGrades is given the time to perform the task. main has to sit around while GetGrades is working.

After that, main decides it's time to find an average. main, being lazy, decides to wait on GetAverage to work out the answer:

Code:

---

average = GetAverage (grades , size);

---

main pretty much doesn't care how this answer comes about, but knows that GetAverage will need the grades array and its size, and knows that GetAverage returns an answer that fits in main's variable called average. main gives GetAverage time to complete its work, while main waits to assign the answer.

Then main dispatches the final task to FindMinMax. That function wants memory locations to store its answers, but promises that when it returns the answers will be correct. Thus explains our signature of FindMinMax:

Code:

---

void FindMinMax (int grades[] , size_t size , size_t *minPos , size_t *maxPos)

---

Because functions can't return more than one thing of a certain type. The main function is also responsible for these locations when it makes the call:

Code:

---

FindMinMax(grades , size , &mindex , &maxdex);

---

After this, main should have all the information it needs to present to the user in average, mindex, maxdex, and grade. These are all variables defined by (initialized in) and local to (belonging to, in the scope of) main. Here main actually does its own work formatting output before it ends the program, or it could dispatch the task again, depending on how you write main. You're the boss!

Actual programs have a lot more complicated flow charts, but it may be a while before you write anything more complicated than "main calls the foo function". It's all part of learning to know why these designs make sense, and basically how simple you can make it so it's free of bugs AND does what you need. There are plenty of tools at hand to implement a procedural program in C++.

GetAverage does not want the size of the array. That's C thinking. GetAverage can easily acquire the size of the array, if it needs it. That's why we use std::tr1::array, not native C arrays.
FindMinMax does not want memory locations to store its answers - it wants variables to store its answers. We use references instead. Plus GetAverage and FindMinMax will not modify the grades; thus the should be const.
More proper prototypes would be:

Code:

---

void GetGrades (std::tr1::array<int, 10>& grades);
double GetAverage (const std::tr1::array<int, 10>& grades);
void FindMinMax (const std::tr1::array<int, 10>& grades, size_t& MinPos, size_t& MaxPos);

---

I'd say you're thinking way too much C. This is the C++ forum. Let's not teach newbies C ways. Let's teach them modern C++ ways instead.

Instead of showing off, how about you explain templates and references to the OP, instead of complaining about how I think.

I'm willing to explain good programming and answer his questions in terms of the things he understands now.

Put simply, I'm not going to explain templates. Just like Accelerated C++, I'm just going to say, this is how you do, and that's enough for now. Know that the syntax of a C++ array is std::tr1::array<T, size> where T is the type the array should hold and size the size of the array.
std::tr1 is the namespace it lies in. This much I can expect the OP to know or should know.
The good thing about C++ arrays is several things, but only one matters now and that is size. The C++ array knows its size, which you can get via the .size() member function.
Plus it has the .at() member function which eliminates those pesky buffer overruns and saves you trouble of undefined behavior.

References is not something I'm going to explain. That's basic of basics. The OP should be aware of them, or open the book to read about them. Or read a tutorial. Without references or basic understanding of pointers, you're not going anywhere. It's simply pointless to code functions if you don't know them.
And if one understand pointers, I would assume one knows references. But not necessarily vice versa.

Thank you for following through.