declare class

[nguyentuandang]

what is declared code in C++

  classA~::classA()

[CodeGoggles]

A declaration means there is code with this name somewhere in the program, the compiler reads in a linear fashion ex: line by line. If it come across a variable that is not declared it doesn't have a clue as to what it actually represents.

void dosomething(); // a declaration, if this statement wasnt here
                    // when main calls the dosomething function the compiler gets confused 
                    // beacuse it hasnt read the definition yet.

int main()
{
	dosomething(); // a function call
}

void dosomething() // a function definition
{

}

The same thing applies for variables, you must declare them before you use them.

[nguyentuandang]

Thanks so much :D