CODEWITHSUNDEEP
c++
user2865835
user2865835

Reputation: 59

C++ "expression must be a modifiable lvalue" error

void Sort(Maximumas Maxi[], int ind){
    int m = 0; // begin
    bool bk = true;
    while(bk){
        bk = false;
        for(int j=ind-1; j>m; j--){
            if(Maxi[j].GetQuantity() > Maxi[j-1].GetQuantity()){
                bk = true;
                int c = Maxi[j].GetQuantity();
                Maxi[j].GetQuantity() = Maxi[j-1].GetQuantity();
                Maxi[j-1].GetQuantity() = c;
            }
        }
        m++;
    }
}

When I try to compile this code I get an error: expression must be a modifiable lvalue

What's wrong with my code?

Upvotes: 0

Views: 819

Answers (2)

juanchopanza
juanchopanza

Reputation: 227390

My guess would be that Maximumas::GetQuantity() returns by value or const reference, so you cannot do this kind of thing:

Maxi[j-1].GetQuantity() = c;

You need an overload that returns a reference. Assuming it returns int, you need something like

int& GetQuantity();
const int& GetQuantity() const;

where the const overload allows you to call the member on const instances or via const references.

Note that unless this is an exercise, it would be simpler to use std::sort with a suitable predicate.

Upvotes: 3

Martin J.
Martin J.

Reputation: 5118

I would need to have the signature of Maximumas::GetQuantity() to be sure, but it looks like this method returns a non-modifiable type, so that you can't assign a value to it, e.g. int or const int&. This would explain why the two following lines fail:

Maxi[j].GetQuantity() = Maxi[j-1].GetQuantity();
Maxi[j-1].GetQuantity() = c;

You should change your method to return a modifiable type, like int&, to make it work.

Upvotes: 1

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