class and header

[xenovia12]

how can i access the functions in header to a class in main.cpp

i mean what is the use of header file if i cannot access it on a class

[Peter87]

Include the header in main.cpp.

[xenovia12]

yea i included it . thats not what i meant.
example

a.h

#ifndef A_H_INCLUDED
#define A_H_INCLUDED

int addition ( int number1 , int number2 ) {
return number1+number2;
}




#endif // A_H_INCLUDED 

main.cpp
#include <iostream>
#include "a.h"
using namespace std;
int addition( int number1 , int number2 );
class Calculator {
int firstnumber;
int secondnumber;
public:
 void operate();
};
void Calculator::operate() {
cout << "Enter number";
cin >> firstnumber >> secondnumber;
addition(firstnumber, secondnumber);
}
int main()
{
Calculator newCalculator;
newCalculator.operate();

}

the error is undefined reference to addition (int , int)

but i already declare the prototype and include the header

[ajh32]

You don't need to declare the prototype as you have it declared in the header that has been included in the source file.

[Peter87]

I have no idea why you get an error. Are you sure this is the same code that gave you the error?

[xenovia12]

@ajh32 oh i see ,about declaring prototype in header
but i think declaring prototype in main instead on header would be more readable

[xenovia12]

@Peter87

yeah this is
why not give me code similar to this

[ajh32]

@ajh32 oh i see ,about declaring prototype in header
but i think declaring prototype in main instead on header would be more readable

No, just remove the line #5 in the source file as you have the function declared and written in the header, at compile time the #include "a.h" is replaced by the contents of the "a.h" file, in your example as if you had written the addition function at line #3 of your source.

[Peter87]

The reason I asked was because when I compile your code it compiles without any problems. Could you please post the full error message that you get?

[xenovia12]

||=== Build: Debug in asd (compiler: GNU GCC Compiler) ===|

obj\Debug\main.o||In function `ZN10Calculator7operateEv':|

C:\Users\Lorence\Desktop\asd\main.cpp|14|undefined reference to `addition(int, int)'|

||=== Build failed: 1 error(s), 0 warning(s) (0 minute(s), 2 second(s)) ===|

[xenovia12]

@ajh32
i see but it doesnt work due to my issue