Quadratic Formula c++ - user-defined function - c++

Question

I wrote this code with a user-defined function, but it seems not to work. I've trying to find out where the mistake is for hours. But couldn't find anything. it looks like the problem is in passing the parameter. But I don't know, I'm pretty new to this!
#include <iostream>
#include <cmath>
using namespace std;
double solutionFun (double a, double b, double c) {
double delta, solution1, solution2;
delta = b*b - 4*a*c;
if (delta > 0 ){
solution1 = (-b + sqrt(delta)) / (2*a);
solution2 = (-b - sqrt(delta)) / (2*a);
cout << "There are 2 solutions." << endl;
cout << "The solutions are:";
return solution1, solution2;
}
else if (delta == 0){
solution1 = (-b) / (2*a);
cout << "There is 1 solution." << endl;
cout << "The solution is:";
return solution1;
}
else {
cout << "There is no solution.";
return 0;
}
}
int main(){
double a ,b ,c;
cout << "Please enter the values of a, b, and c respectively:";
cin >> a ,b ,c;
solutionFun(a ,b ,c);
return 0;
}

Answer 1

A few issues with regards to code validity and desired behavior (coding practice/design aside):
See how to return multiple values from your solutionFun() (currently defined to return double) by using std::vector -- even though you are not using anything returned in this piece of code.
You didn't print (cout <<) the solution values themselves, and it seemed like you were going for it.
See how to use std::cin for multiple inputs in one line of code.
A fixed version -- with respect to the above points:
#include <iostream>
#include <cmath>
#include <vector>
using namespace std;
std::vector<double> solutionFun (double a, double b, double c) {
double delta, solution1, solution2;
delta = b*b - 4*a*c;
if (delta > 0 ){
solution1 = (-b + sqrt(delta)) / (2*a);
solution2 = (-b - sqrt(delta)) / (2*a);
cout << "There are 2 solutions." << endl;
cout << "The solutions are: " << solution1 << " and " << solution2;
return {solution1, solution2};
}
else if (delta == 0){
solution1 = (-b) / (2*a);
cout << "There is 1 solution." << endl;
cout << "The solution is: " << solution1;
return {solution1};
}
else {
cout << "There is no solution.";
return {};
}
}
int main(){
double a ,b ,c;
cout << "Please enter the values of a, b, and c respectively:";
cin >> a >> b >> c;
auto result = solutionFun(a ,b ,c);
for (auto scalar : result)
{
// Do something with a component, or don't return anything from the function : )
}
return 0;
}

Answer 2

This code is not how you get multiple inputs:
cin >> a ,b ,c;
Instead, you want:
cin >> a >> b >> c;
This code is not how you display answers:
cout << "The solutions are:";
return solution1, solution2;
Instead you want:
cout << "The solutions are:" << solution1 << " and also " << solution2;

Answer 3

Another method is pass your solution variables on the command line:
void solutionFun (double a, double b, double c,
double& solution1, double& solution2, size_t& solution_count) {
double delta;
delta = b*b - 4*a*c;
solution2 = 0.0;
if (delta > 0 ){
solution1 = (-b + sqrt(delta)) / (2*a);
solution2 = (-b - sqrt(delta)) / (2*a);
solution_count = 2;
cout << "There are 2 solutions." << endl;
cout << "The solutions are: " << solution1 << " and " << solution2;
return;
}
else if (delta == 0){
solution1 = (-b) / (2*a);
solution_count = 1;
cout << "There is 1 solution." << endl;
cout << "The solution is: " << solution1;
return;
}
else {
cout << "There is no solution.";
solution_count = 0;
return;
}
}
The solution1, solution2 and solution_count are passed by reference which means that the function can modify the caller's variables.