CODEWITHSUNDEEP
c++compiler-errorsoperators
jacob1031
jacob1031

Reputation: 5

c++ error: no match for ‘operator-=’

I am fairly new to c++. As a project I was rewriting a little game I wrote in python (I never got it to work correctly). During compilation I get this error: error: no match for ‘operator-=’

I know that this operator exists in c++, so why am i getting this error?

code:

void rpg() {
    cout << "This mode is not yet complete. It only contains a dungeon so far. I'm still working on the rest!";
    dgn();
}
void dgn() {
    int whp = 100;
    int mahp = 100;
    int hhp = 100;
    string m;
    int mhp;
    cout << "There are three passages. Do you take the first one, the second one, or the third one? (Give your answer in numbers)";
    int psg;
    cin >> psg;
    switch (psg) {
    case 1:
        m = "Troll";
        mhp = 80;
        break;
    case 2:
        m = "Goblin";
        mhp = 35;
        break;
    case 3:
        m = "Dragon";
        mhp = 120;
    }
    cout << "A ";
    cout << m;
    cout << " appears!";
    dgnrd(m, mhp, whp, mahp, hhp);
}

void dgnrd(string m, string mhp, int whp, int mahp, int hhp) {
    bool alive = true;
    while (alive) {
        string wa;
        string ma;
        string ha;
        cout << "What does Warrior do? ";
        cin >> wa;
        cout << "What does Mage do? ";
        cin >> ma;
        cout << "What does Healer do? ";
        cin >> ha;
        if (wa == "flameslash") {
            cout << "Warrior used Flame Slash!";
            mhp -= 20;
        }
        else if (wa == "dragonslash" && m == "Dragon") {
            cout << "Warrior used Dragon Slash!";
            mhp -= 80;
        }
        else if (wa == "dragonslash" && (m == "Troll" || m == "Goblin")) {
            cout << "Warrior's attack did no damage!";
        }
        if (ma == "icicledrop") {
            cout << "Mage used Icicle Drop!";
            mhp -= 30;
            mahp -= 10;
            whp -= 10;
            hhp -= 10;
        }
        else if (ma == "flamesofhell") {
            cout << "Mage used Flames of Hell!";
            mhp -= 75;
            mahp -= 50;
            whp -= 50;
            hhp -= 50;
        }
        else if (ma == "punch") {
            cout << "Mage used Punch!";
            mhp -= 5;
        }
    }
}

Upvotes: 0

Views: 558

Answers (3)

Ben Voigt
Ben Voigt

Reputation: 283634

In dgn(), you have

int mhp;

which is sensible, because it is a numeric quantity.

But then your helper function declares

string mhp

in the argument list, which should have caused a type mismatch error between actual and formal parameters in the function call 

dgnrd(m, mhp, whp, mahp, hhp);

Fix that to int& mhp and several problems will go away at once.

Note that & which creates a reference. This makes the function share the variable with its caller, so that changes are made to the caller's copy. Otherwise (in pass-by-value) all changes inside the function simply disappear when the function returns.

Upvotes: 2

Juned Ahsan
Juned Ahsan

Reputation: 68715

It seems you are running the -= operator on a string instead of int. mhp is a string and hence the following statements is causing compilation error:

mhp -=

Upvotes: 0

juanchopanza
juanchopanza

Reputation: 227420

The reason is that std::string has no operator -=. There is +=, which appends to an existing string, but the semantics of an operator -= wouldn't be clear.

Besides that obvious problem, the types of the parameters of dgnrd function do not match those of the arguments you pass it.

Upvotes: 1

Related Questions