Passing by reference

[klharding2]

Hello, this is a homework problem, but I can't find the problem with my program. My TA who is supposed to help me couldn't figure it out either. -.- First of all, I know there is a problem with the factorials. It only outputs the right answer up to n=6 for the sin function and n=10 for the exponential function. I'm avoiding that issue until I resovle this one. The problem I'm trying to figure out is with passing the values by reference. When I call the values from the main function, all of the 'finalvalue' answers that were previously correct are changed. Any help is sincerely appreciated! I am just learning C++ and this is my first attempt with functions so please be simple.

#include <iostream>
#include <cmath>

using namespace std;
double factorial(int);
void sin (double, int, double&);
void exponential (double, int, double&);

int main ()
{
    int choice, n;
    double x, finalvalue;
    cout<<"Select the function you wish to evaluate." <<endl;
    cout<<"1) sin x" <<endl;
    cout<<"2) e^x" <<endl;
    cin>>choice;
    cout<<"Enter the value of x you wish to evaluate." <<endl;
    cin>>x;
    cout<<"Enter the number of terms in the series." <<endl;
    cin>>n;

    if(choice==1) {
    sin(x,n,finalvalue); 
    cout<<finalvalue <<endl;
    }

    else if (choice==2) {
    exponential(x,n,finalvalue);
    cout<<finalvalue <<endl;
    }

    else {
    cout<<"You have entered an incorrect value. Please enter 1 or 2." <<endl;
    }

    system ("PAUSE");
    return 0;
}    


double factorial(int n)
{
        int i=0, fact=1;
        if(n<=1)
        {
                return(1);
        }
        else
        {
            for (i=1; i<=n; i++)
            {
                fact=fact*i;
            } 
        return(fact);
        }
}

void sin (double a,int b,double& finalvalue) {
     int i;
     double f=-1;
     double answer, q, z;
     for(i=0; i<=b; i++)
     {
     q=((2*i)+1);
     z=factorial(q);
     cout<<z <<endl;
     answer=(pow(f,i)/z)*pow(a,q);
     cout<<answer <<endl;
     finalvalue+=answer;  
     cout<<finalvalue <<endl;
     }
     return; }

void exponential (double a, int b, double& finalvalue) {
     int i;
     double z, answer;
     for (i=0; i<=b; i++)
     {
     z=factorial(i);
     cout<<z <<endl;
     answer=pow(a,i)/z;
     cout<<answer <<endl;
     finalvalue+=answer;
     cout<<finalvalue <<endl;
     }
     return; }

[deceptikon]

Well, one obvious problem is that your factorial function may return a double, but it uses an int internally to calculate the factorial. Therefore you're still limited to the range of a signed integer.

[mike_2000_17]

The problem is that you never initialize the value of "finalvalue", neither in the main() function nor in the sin/exp functions. You should simply add finalvalue = 0.0; at the beginning of each function (sin and exponential), and that should solve your problem. The rest looks fine to me.

[klharding2]

Ahhh thank you so much! My teacher is horrible but I learn so much from this site!!