CODEWITHSUNDEEP
c++class
Daniel Marhuenda
Daniel Marhuenda

Reputation: 11

c++ expression must be a modifiable lvalue Classes

I was doing the foundation of a class program and I was trying to modify the value of an object of the class: In the main.cc:

#include <iostream> 
#include "ComputeInt.h" 
main() 
{  ComputeInt computation; 
   computation.real() = 5; 
   computation.operator=(Factorial(computation)); 
}

In the .h:

#include <iostream> 
#ifndef ComputeInt_H 
#define ComputeInt_H 
class ComputeInt
{  public: 
     int real();
}; 
ComputeInt Factorial(const ComputeInt& computation); 
#endif

In the .cc:

#include <iostream> 
#include "ComputeInt.h" 
ComputeInt Factorial(const ComputeInt& computation) 
{  ComputeInt result = computation.real() +1;
   return result; 
}

I get an error that says expression must be a modifiable lvalue, and if I try to use make I get

conversion from ‘int’ to non-scalar type ‘ComputeInt’ requested

I don´t know why it doesn´t work, computation.real is a int and so it should be able to use +1.

Thanks in advance

Upvotes: 1

Views: 148

Answers (3)

user12002570
user12002570

Reputation: 1

In your current program real is a member function of the class ComputeInt and not a data member. So you can solve this issue as shown below:

.h

#ifndef ComputeInt_H 
#define ComputeInt_H
class ComputeInt
{  public: 
     int real;//removed () here. This means real is a data member now
};
ComputeInt Factorial(const ComputeInt& computation);
#endif

.cpp

#include "ComputeInt.h" 
ComputeInt Factorial(const ComputeInt& computation) 
{  ComputeInt result ; //create object of type ComputeInt
   result.real= computation.real +1; //note result.real at the left hand side
   return result; 
}

main.cpp

#include "ComputeInt.h" 
#include<iostream>
int main() 
{  ComputeInt computation; 
   computation.real = 5; 
   
   ComputeInt computation2;
   computation2.real = 10;
   
   computation.operator=(Factorial(computation2)); 
   std::cout<<computation.real;//this prints 11
}

The output of the program can be seen here.

Upvotes: 2

Karol T.
Karol T.

Reputation: 653

Method real() returns integer by value so if you do:

computation.real() = 5;

you try to assign value "5" to another value. It is not possible, similarly like you are not allowed to do:

3 = 5;

conversion from ‘int’ to non-scalar type ‘ComputeInt’ requested

There is no known conversion from int you created by real()+1 to ComputeInt (you don't have constructor and/or operator=)

Upvotes: 2

Hurried-Helpful
Hurried-Helpful

Reputation: 2000

int real() is defined as a class method (function) that returns an int, not an int itself.

If you want to make it an int, make it int real without the ().

Upvotes: 1

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