C++ Error in program compiling

Question

Why is this c++ program giving me errors:

#include <iostream>
using namespace std;

int main (){
    NumbersClass num;       
    num.setNumbers(1);          
}

class NumbersClass
    {
    public:
        NumbersClass() {}           
        void setNumbers(int i) { }          
    };

Here are my errors:

taskbcplus.cpp(7): error C2065: 'NumbersClass' : undeclared identifier
taskbcplus.cpp(7): error C2146: syntax error : missing ';' before identifier 'num'
taskbcplus.cpp(7): error C2065: 'num' : undeclared identifier
taskbcplus.cpp(9): error C2065: 'num' : undeclared identifier
taskbcplus.cpp(9): error C2228: left of '.setNumbers' must have class/struct/union
1>          type is ''unknown-type''

In C++, you at least need a declaration before use (this is different than C#, for example). — crashmstr
– crashmstr, Commented Nov 4, 2013 at 17:11
@crashmstr In this case, you need the class definition too, since you are instantiating it in main. — juanchopanza
– juanchopanza, Commented Nov 4, 2013 at 17:14
@juanchopanza Correct, but you don't need the implementation details (i.e. the definitions could be left for after main instead of inline with the class). — crashmstr
– crashmstr, Commented Nov 4, 2013 at 17:17
@crashmstr Correct. You need the class definition, but not the definition of the member functions. — juanchopanza
– juanchopanza, Commented Nov 4, 2013 at 17:17

juanchopanza · Accepted Answer · 2013-11-04 17:09:38Z

5

You need to put the NumberClass definition before the point at which you first instantiate it, i.e. before main.

class NumbersClass
{
public:
    NumbersClass() {}           
    void setNumbers(int i) { }          
};

int main (){
    NumbersClass num;       
    num.setNumbers(1);          
}

answered Nov 4, 2013 at 17:09

juanchopanza

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