CODEWITHSUNDEEP
c++incrementdecrement
liliaceae
liliaceae

Reputation: 9

invalid operands of types ‘double’ snd const char [3]’ to binary 'operator<<'

This is the error message I get when I try to build:

invalid operands of types ‘double’ snd const char [3]’ to binary 'operator<<'

Obviously I'm really new to this. Any help would be appreciated.

The code reads:

 #include <iostream>
 using namespace std;


 int main () 
 {
     double x = 3;
     double y = 4;

     cout << "(" << x = y++ << ", " << y << ")" << endl;
     cout << "(" << x = ++y << ", " << y << ")" << endl;
     cout << "(" << x = y-- << ", " << y << ")" << endl;
     cout << "(" << x = --y << ", " << y << ")" << endl;

         return 0;
 }

Upvotes: 0

Views: 1790

Answers (2)

Mike Seymour
Mike Seymour

Reputation: 254701

Assignment (=) has a lower precedence than shift (<<), so you need parantheses to get the meaning you expect:

cout << "(" << (x = y++) << ", " << y << ")" << endl;
               ^       ^

But you shouldn't be writing code with multiple side-effects like this: the evaluation order of the operands isn't specified, and this sort of thing can easily lead to undefined behaviour. Keep your code simple, doing one thing at a time.

Upvotes: 0

Yu Hao
Yu Hao

Reputation: 122493

= has a lower precedence than <<, change it to:

std::cout << "(" << (x = y++) << ", " << y << ")" << std::endl;
//                  ^       ^

See C++ Operator Precedence.

Upvotes: 1

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