Switch statement not working c++ and D:\c++ dev-c\Makefile.win recipe for target 'abc.o' failed

Question

So, I continued working on my abc formula in c++, and yet again, some errors pop up :D

this is what I have now:

#include <iostream>
#include <cmath>
using namespace std;

class abcformule{
    public:
        int discriminant(double a, double b, double c) {
            return pow(b, 2) - 4 * a *c;
        }

        void answer(double a2, double b2, double c2) {
            int D = discriminant(a2, b2, c2);
            switch(D) {
                case < 0:
                    cout << "Discriminant is lower than 0, no solutions for x.";
                    cout << endl;
                    break;
                case > 0:
                    cout << "Discriminant is bigger than 0, two solutions for x: ";
                    cout << endl; 
                    cout << "x = " << (-b2 + sqrt(D)) / (2 * a2) <<
                            " or " << (-b2 - sqrt(D)) / (2 * a2) << 
                            "." << endl;
                    break;
                case = 0:
                    cout << "Discriminant is 0, only one solution for x: " << endl;
                    cout << (-b2) / (2 * a2) << endl;
            }
        }
};

int main(int argc, char** argv) {
    abcformule abc;
    abc.answer(5, -2, -7);
    return 0;
}

And these are the errors:

D:\c++ dev-c\abc.cpp    In member function 'void abcformule::answer(double, double, double)':
14  10  D:\c++ dev-c\abc.cpp    [Error] 'D' cannot appear in a constant-expression
18  10  D:\c++ dev-c\abc.cpp    [Error] expected primary-expression before '>' token
25  10  D:\c++ dev-c\abc.cpp    [Error] expected primary-expression before '=' token
25  12  D:\c++ dev-c\abc.cpp    [Error] an assignment cannot appear in a constant-expression

How do I fix this? Oh, and I saw this thing pop up in the error log too:

28      D:\c++ dev-c\Makefile.win   recipe for target 'abc.o' failed

You need to revisit how case statements work: http://en.cppreference.com/w/cpp/language/switch — NathanOliver, Apr 18 '18 at 18:19
A `case` must be a compile-time constant value. It can't be a condition. This should really be an `if {} else if {} else {}`. — François Andrieux, Apr 18 '18 at 18:23
Please get yourself [a good C++ book](https://stackoverflow.com/q/388242/10077). — Fred Larson, Apr 18 '18 at 18:26
"D:\c++ dev-c\Makefile.win recipe for target 'abc.o' failed" simply means that because of the previously listed errors in your code the program could not be built. — user4581301, Apr 18 '18 at 18:29

score 0 · Accepted Answer · edited Apr 18 '18 at 19:31

I prefer you to use if else instead of switch because you cann't do comparisons in cases in switch

#include <iostream>
#include <cmath>
using namespace std;

class abcformule{
public:
    int discriminant(double a, double b, double c) {
        return pow(b, 2) - 4 * a *c;
    }

    void answer(double a2, double b2, double c2) {
        int D = discriminant(a2, b2, c2);

            if(D<0){
                cout << "Discriminant is lower than 0, no solutions for x.";
                cout << endl;
            } else if(D>0){
                cout << "Discriminant is bigger than 0, two solutions for x:     ";
                cout << endl; 
                cout << "x = " << (-b2 + sqrt(D)) / (2 * a2) <<
                        " or " << (-b2 - sqrt(D)) / (2 * a2) << 
                        "." << endl;
            } else{
                cout << "Discriminant is 0, only one solution for x: " <<          endl;
                cout << (-b2) / (2 * a2) << endl;
            }   
    }
};

int main(int argc, char** argv) {
    abcformule abc;
    abc.answer(5, -2, -7);
    return 0;
}

The inconsistent indentation and seemingly random addition of white space (include in a string literal) bother me more than I would have expected. — François Andrieux, Apr 18 '18 at 18:27

Switch statement not working c++ and D:\c++ dev-c\Makefile.win recipe for target 'abc.o' failed

1 Answers1