error: two or more data types in declaration of main?

c++ function if-statement while-loop declaration

20,196

Solution 1

None of that code is valid. You begin a class definition with class OperateClass, but never end it and run right into main. A (simplified) class definition takes the form of:

class [name] {

};  // semi-colon terminates definition

// so...

class OperateClass {

};

Next, you declare main... but it leads to an else branch (?).

int main()
{

    cout << "Do you want to add, subtract, multiply or divide? I want to : " << endl;
    cin >> ans;

    if(ans == "add"){
    OperateClass opOper;
    opOper.add();

}else{  // what is this?

Functions must also terminate via their closing brace, i.e.,

int main() {

}  // function is over!

Now it looks like those may just be copy/paste errors. If that's the case then you probably just forgot the semi-colon at the end of the class definition.

Solution 2

Consider the following program:

class C

int main() {

}

class C {

}

void someFunc(){}

This is basically your program boiled down to the necessities. Here are the errors:

error: two or more data types in declaration of 'main'
error: expected ';' after class definition

Here's the corrected code:

class C; //<--semicolon in forward declaration

int main() {

}

class C {

}; //<--semicolon after class definition

void someFunc(){}

Solution 3

Lets make a slight modification of your code so that your syntax is right.

int main()
{

    cout << "Do you want to add, subtract, multiply or divide? I want to : " << endl;
    cin >> ans;

    if(ans == "add"){
    OperateClass opOper;
    opOper.add();
        }

else if (ans == "subtract"){
    OperateClass opOper;
    opOper.subtract();
        }

else if (ans == "multiply"){
    OperateClass opOper;
    opOper.multiply();
        }

else if(ans == "divide"){
    OperateClass opOper;
    opOper.divide();

        }
else {} 

} //end of main

Your class variable declaration statement "OperateClass opOper" also repeats in each case, you could also just write that statement outside your if-else conditions to avoid repetition since that statement is true regardless of any case.

20,196

Author by

Bucky763

Updated on July 09, 2022

Comments

Bucky763 almost 2 years

Very new to coding, so please be understanding ;)

I'm basically trying to make a calculator using the while loop, and if statements.

#include <iostream>

using namespace std;

int x = 1;
int number;
int total = 0;
int amt = 1;
int a;
int b;
int c;
int d;
string ans;

class OperateClass

I get the error: two or more data types in declaration of 'main'

Please explain what this means/how to fix it.

I was also wondering if I need to make a new object for each function (Add, subtract, multiply, and divide)

Please help!

int main()
{

    cout << "Do you want to add, subtract, multiply or divide? I want to : " << endl;
    cin >> ans;

    if(ans == "add"){
        OperateClass opOper;
        opOper.add();

    }else{

        if(ans == "subtract"){
            OperateClass opOper
            opOper.subtract();
                }

    }else{

        if(ans == "multiply"){
            OperateClass opOper
            opOper.multiply();
        }

    }else{

        if(ans == "divide"){
            OperateClass opOper
            opOper.divide();

        }
    }

}

class OperateClass{
    public:
        int add(){
            while(x <= 3){
                cout << "Enter a number to use to add: " << endl;
                cin >> a;
                total = total + a;
                x++;
                amt++;
            }
        }

        int subtract(){
            while(x <= 3){
                cout << "Enter a number to use to add: " << endl;
                cin >> b;
                total = total - b;
                x++;
                amt++;
            }
        }

        int multiply(){
            while(x <= 3){
                cout << "Enter a number to use to add: " << endl;
                cin >> c;
                total = total * c;
                x++;
                amt++;
            }
        }

        int divide(){
            while(x <= 3){
                cout << "Enter a number to use to add: " << endl;
                cin >> d;
                total = total / d;
                x++;
                amt++;
            }
        }
}

int print(){
    cout << "Your total is: " << total << endl;

    return 0;
}

Lwin Htoo Ko almost 12 years

you should use if-else if-else or switch. what you are doing now is confusing. difficult to find open and close brace.
chris almost 12 years

Those global variables all over the place are really not a good idea.
Lwin Htoo Ko almost 12 years

In "if(ans == "subtract"/"multiply"/"divide")" you forget ";" after "Operate Class opOper"
Bucky763 almost 12 years

Alright, I'm no longer getting the semicolon errors
Bucky763 almost 12 years

Now I'm getting error: aggregate 'OperateClass opOper' has incomplete type and cannot be defined. How would this be corrected?
chris almost 12 years

@Bucky763, Just kill the class OperateClass; and move the whole class there instead.
Keith Thompson almost 12 years

The usual way to write an if / else if / sequence is to treat the "else if" as if it were a single word. I can't format it correctly in a comment, but this gist shows the more traditional way to do this. (Some languages even have elsif or elseif as a keyword; C++ doesn't.)
chris almost 12 years

A switch would work well here too.
Bucky763 almost 12 years

Ok I moved the Class definition before the main. The program runs now!
Bucky763 almost 12 years

Now im wondering how to get cout << "Your total is: " << total; to run

chris almost 12 years

There's a hidden if. It's there, though.
Ed S. almost 12 years

@chris: Yeah that's why I added that last bit on. I think a missing semi-colon is probably the issue and this was just a bad copy/paste job.
Bucky763 almost 12 years

Alright. I'm going to edit the original code and add the semicolons.
Bucky763 almost 12 years

Now I'm getting the error: aggregate 'OperateClass opOper' has incomplete type and cannot be defined
Keith Thompson almost 12 years

@Bucky763: Please don't do that. With the code corrected, the question no longer makes sense. I'll roll back the edit for you.
chris almost 12 years

Well I think it's been determined now that the problem was semicolons, which are in here among other things. Upvote for ya.
chris almost 12 years

Just kill the class OperateClass; and move the whole class there instead.
Bucky763 almost 12 years

Moving the class def before main got the program to run!
Bucky763 almost 12 years

The only thing is, it wont run this function I added void print(){ cout << "Your total is: " << total << endl; }
chris almost 12 years

@Bucky763, A new question completely is more suited for further problems, but as a random guess, did you ever call it?
Bucky763 almost 12 years

Ill make a new question. Thanks. And can you give an example of calling it?
Bucky763 almost 12 years

I think I forgot that. Adding it to main should be fine?
chris almost 12 years

@Bucky763, Wherever you want the printing to occur.