'double' division problem?

[acevans2]

I have this program that is similar to my last, but uses functions instead.

I am having the problem of displaying 0.00 for all my outcomes. Why is this? I keep getting hung up on simple problems like this.


EDIT EDIT: Ok, I changed the datatype of the variables being passed to calcScore to double's and now it displays a number... but the number isn't exactly right. Why does it give me like 99.62 when I pass it perfect scores?




Here's my code:

Line 71-90 is where I bet the problem is... calculating those score outputs.

#include<iostream>
#include<cmath>
#include<iomanip>

using namespace std;


double programavg = 0;
double programscores = 0;
double programmax;

double quizavg = 0;
double quizscores = 0;
double quizmax;

double testavg = 0;
double testscores = 0;
double testmax;

char choicemore = 'y';
double examavg;
double overallavg;

/* This is the getIntSum function */ 


int getIntSum(string s, int exitVal)
{
int addpoints;
int totalpoints = 0;;

	while (addpoints!=exitVal)
	{
		cout << s << exitVal << " to quit):";
		cin >> addpoints;
		
		
		totalpoints+=addpoints;
	}
	
		cout << endl;
		return totalpoints;
	
	
}


/* This is the getPromptedInt function */

int getPromptedInt(string s, int min, int max)
{
int maxpoints;

cout << s << min << "..." << max << "):"; 
cin >> maxpoints;
cout << endl;

	while (maxpoints>max || maxpoints<min)
	{
		cout << "Error: value must be between " 
		<< min << " and " << max << ". Please re-enter:";
		cin >> maxpoints;
		cout << endl;
	}

		return maxpoints;
	
	
}

/*This is the calcScore function */

double calcScore(double sum, double maxPoss)
{

double finalscore;

	if (maxPoss>0)
	{
		finalscore = (sum / maxPoss);
		finalscore*=100;

		return finalscore;
	}
	else
	{
		return 0;
	}

}


/* This is the main function --------------------*/

int main()
{
/* This loop is for the purpose of repeating while the user wants to */


while (choicemore=='y')
{
programmax = getPromptedInt("Enter the maximum possible program points (", 0, 1200);
programscores = getIntSum("Enter a program score (", -1);

quizmax = getPromptedInt("Enter the maximum possible quiz points (", 0, 120);
quizscores = getIntSum("Enter a quiz score (", -1);

testmax = getPromptedInt("Enter the maximum possible test points (", 0, 300);
testscores = getIntSum("Enter a test score (", -1);


programavg = calcScore(programscores, programmax);
quizavg = calcScore(quizscores, quizmax);
testavg = calcScore(testscores, testmax); 


cout << fixed << setprecision(2) << "Program average is: " << programavg;
cout << fixed << setprecision(2) << endl << "Quiz average is " << quizavg;
cout << fixed << setprecision(2) << endl << "Test average is: " << testavg;

//  The following loop is to calculate the exam average
	if (testavg==0)
	{
		examavg = quizavg;
		cout << setprecision(2) << fixed << endl << "Exam average is: " << examavg;
	}
	else
	{
		examavg = ((((testavg * 3) + quizavg)) / 4);
		cout << setprecision(2) << fixed << endl << "Exam average is: " << examavg;
	}	
	
// This loop is for displaying the Overall average

	if (testavg==0)
	{	 
		overallavg = ((.6*quizavg) + (.4*programavg));
		cout << endl << "Overall average is: " << overallavg;
	}
	else
	{
		overallavg = ((.4*programavg) + (.15*quizavg) + (.45*testavg));
		cout << endl << "Overall average is: " << overallavg;
	}
	

// This next loop is the warning message for low test scores
	if (examavg<55)
	{
		cout << endl << endl << "*** Your exam average is below 55%! ***" << endl;
	}
	else
	{
	cout << endl;
	}	   
	
cout << endl << "Another (y/n)? ";
cin >> choicemore;
cout << endl;

}

return 0;

}

[acevans2]

Someone PLEASE help me? I can't imagine it's some major issue.

[int main]

I am surprised that your program does compile.
In line 80 you write
finalscore = (sum / maxPoss);

But I do not see where you define and initilize your variable sum.
And if something is 0, the result of its division is 0 as wel.

int main

[bluegray]

But I do not see where you define and initilize your variable sum.
double calcScore(double sum, double maxPoss)

I was playing around with your code and can't seem to figure out the problem either, so i am interested to see where the problem is too.

[firedraco]

Well, it is most likely the fact that double division sucks, if you do seemingly simple stuff (divide by ints, etc) it usually has lots of problems...like the 99.67 instead of 100. It is most likely because of the avgs*.4/.6 that is screwing it up. You could try couting the avgs as they are made for a debug, and see if they are glitched in some way. If they are, it is probably because of double errors.

[exception]

Someone PLEASE help me? I can't imagine it's some major issue.

Wow. You waited like... an WHOLE HOUR before bumping your post. How rude of all the people here not to be waiting for the possibility to answer your questions ASAP.

Why does it give me like 99.62 when I pass it perfect scores?

What should the output be? What influences it? In line 73, what values do 'sum' and 'maxPoss' have?

Well, it is most likely the fact that double division sucks

Yeah, right. I don't understand it, I've heared that it might be wrong sometimes, so it sucks - how obvious. As I argued in my article about double arithmetic (http://www.cplusplus.com/forum/articles/3827/), there *are* problems with it. But to get a noticable error when not performing (in)equlity tests that has any significance, you have to perform quite some calculations or have very "ugly" numbers. So if the result should be 100, getting 99.62 as the result would require the formula x = (a/b)*100 to have (a/b) in the order of 2⁴⁵ or somewhere near that. Is that the case? I doubt it.