C++: void value not ignored as it ought to be [closed] - c++

Question

Closed. This question needs debugging details. It is not currently accepting answers.
Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question.
Closed 7 years ago.
Improve this question
The error is with:
estimate1 = leibnizPi (nTerms, estimatedV1);
&
estimate2 = wallisPi (nTerms, estimatedValue2);
I'm thinking it has to do with the way it is set up to reference the estimatedValue in the function, or the way it is being called is incorrect.
Any help is much appreciated!
NOTE: HAS TO REMAIN VOID. Sorry about that.
#include <iostream>
#include <cmath>
//
// This program will be used in the second assignment (functions)
//
using namespace std;
const double PI = 3.14159265358979323846;
void leibnizPi (int numberofterms, double &estimatedValue1 )
{
double sign = 1.0;
double sum = 0.0;
for (int i = 0; i < numberofterms; ++i) {
double denominator = 2.0 * i + 1.0;
double term = 4.0 / denominator;
sum = sum + sign * term;
sign = -sign;
}
estimatedValue1 = sum;
}
void wallisPi (int numberofterms, double &estimatedValue2)
{
double product = 1.0;
for (int i = 1; i < numberofterms; ++i) {
double r = 2.0*i;
r = r*r;
double term = r/(r-1.0);
product = product * term;
}
estimatedValue2 = 2.0 * product;
}
double abstractError (double computedValue);
double relativeError (double computedValue);
int main (int argc, char** argv) {
double estimate1 = 0;
double absErr1 = 0;
double relErr1 = 0;
double estimate2 = 0;
double absErr2 = 0;
double relErr2 = 0;
double estimatedV1 = 0;
double estimatedValue2 = 0;
for (int nTerms = 1; nTerms < 100001; nTerms = nTerms * 4) {
// Estimate Pi by two different methods
// Leibniz' sum
estimate1 = leibnizPi (nTerms, estimatedV1);
absErr1 = abstractError (estimate1);
relErr1 = relativeError (estimate1);
// Wallis' product
estimate2 = wallisPi (nTerms, estimatedValue2);
absErr2 = abstractError (estimate2);
relErr2 = relativeError (estimate2);
cout << "After " << nTerms << " terms\n";
cout << "Leibniz' estimate: "<< estimate1 << "\n";
cout << "Absolute error: " << absErr1
<< "\tRelative error: " << relErr1
<< "\n";
cout << "Wallis' estimate: "<< estimate2 << "\n";
cout << "Absolute error: " << absErr2
<< "\tRelative error: " << relErr2
<< "\n";
cout << endl;
}
return 0;
}
double abstractFunction (double computedValue)
{
double abstractError = abs(computedValue - PI);
return abstractError;
}
double relativeFunction (double computedValue){
double relativeError1 = abs(computedValue - PI) / PI;
return relativeError1;
}

Answer 1

You cannot use the return value of a function returning void, because there isn't one. Instead, you may want to try something like this:
double leibnizPi (int numberofterms, double &estimatedValue1 )
{
double sign = 1.0;
double sum = 0.0;
for (int i = 0; i < numberofterms; ++i) {
double denominator = 2.0 * i + 1.0;
double term = 4.0 / denominator;
sum = sum + sign * term;
sign = -sign;
}
estimatedValue1 = sum;
return estimatedValue1;
}
double wallisPi (int numberofterms, double &estimatedValue2)
{
double product = 1.0;
for (int i = 1; i < numberofterms; ++i) {
double r = 2.0*i;
r = r*r;
double term = r/(r-1.0);
product = product * term;
}
estimatedValue2 = 2.0 * product;
return estimatedValue2;
}
If you must use a void function, you should assign the variable passed as a parameter (estimatedV1) to the secondary variable (estimate1). Like so:
leibnizPi (nTerms, estimatedV1);
estimate1 = estimatedV1;

Answer 2

No, the problem is that you haven't defined your functions to return anything, and than you try to take what they return (which is undefined) and assign it to a variable, which is a mistake.
Define it as such double leibnizPi (int numberofterms, double &estimatedValue1 )
And add a return statement.
If you can't change the return type of the function, than don't try to treat it as returning a value. Just write leibnizPi (nTerms, estimatedV1); instead of estimate1 = leibnizPi (nTerms, estimatedV1);