order of operations

[moot1]

does c++ know order of operations i want to make this calculator be able to use more than one operation in a math problem.how do i do that?

#include <iostream>
#include <cstdlib>

using namespace std;

class operations
{
    public:

int add()
{
    int Total = 0;
	int Amount;
	int Number;
	int whatoperation;
	int answertoaverage;
	int restart;
    cout << "Enter in how many numbers you want to use" << endl;
	cin >> Amount;

	for(int i = 0; i < Amount; i++)   // Keeps looping until i == Amount
	{
		cout << "Number " << i << ": " ;  // Shows user what number they are entering
		cin >> Number;

		Total = Number + Total;  // Adds number to total
	}

	cout << "The total is " << Total << endl;  // Prints out total value when loop has finished
	Total = 0;  // resets total back to zero

}

int subtract()
{
    int Total = 0;
	int Amount;
	int Number;
	int whatoperation;
	int answertoaverage;
	int restart;

    cout << "Enter in how many numbers you want to use" << endl;
	cin >> Amount;

	for(int i = 0; i < Amount; i++)
	{
		cout << "Number " << i << ": " ;
		cin >> Number;

		if(i == 0)
		{
			Total = Total + Number;
		}

		else
		{
			Total = Total - Number;
		}
	}

	cout << "The total is " << Total << endl;
	Total = 0;
}

int multiply()
{
    int Total = 0;
	int Amount;
	int Number;
	int whatoperation;
	int answertoaverage;
	int restart;

    cout << "Enter in how many numbers you want to use" << endl;
	cin >> Amount;

	for(int i = 0; i < Amount; i++)
	{
		cout << "Number " << i << ": " ;
		cin >> Number;

		if(i == 0)
		{
			Total = Total + Number;
		}

		else
		{
			Total = Total * Number;
		}
	}
	cout << "The answer is " << Total << endl;
    Total = 0;
}

int divide()
{
    int Total = 0;
	int Amount;
	int Number;
	int whatoperation;
	int answertoaverage;
	int restart;

    cout << "Enter in how many numbers you want to use" << endl;
	cin >> Amount;

	for(int i = 0; i < Amount; i++)
	{
		cout << "Number " << i << ": " ;
		cin >> Number;

		if(i == 0)
		{
			Total = Total + Number;
		}

		else
		{
			Total = Total / Number;
		}
	}
	cout << "The total is " << Total << endl;
	Total = 0;
}

int average()
{
    int Total = 0;
	int Amount;
	int Number;
	int whatoperation;
	int answertoaverage;
	int restart;


}

};



int main()
{

    operations callfunctions;

    int Total = 0;
	int Amount;
	int Number;
	int whatoperation;
	int answertoaverage;
	int restart;

	do{

    system("CLS");

	cout << "Here are your choices(enter the number before the operation)" << endl << endl;
	cout << "1.Addition" << endl;
	cout << "2.Subtraction" << endl;
	cout << "3.Multiplication" << endl;
	cout << "4.Division" << endl;
	cout << "5.Average Calculator" << endl;

	cin >> whatoperation;

	system("CLS");

	switch(whatoperation){
    case 1:
    callfunctions.add();
	break;

	case 2:
    callfunctions.subtract();
	break;

	case 3:
    callfunctions.multiply();
	break;

	case 4:
    callfunctions.divide();
	break;

	case 5:
    callfunctions.average();
	break;
	}
	cout << "Enter 1 to restart or 2 to quit: ";
	cin >> restart;


	}while(restart == 1);

    cin.get();
	return 0;
}

[hamsterman]

C++, standard libraries aside, only knows as much as you do. If you want to make 2+3*4 work, you'll have to put some effort into it. If you only want expressions like this, it's quite simple. Find an operator of lowest precedence and split the string at that point. Then calculate the two halves, look at what operator you had and perform the operation. The algorithm is recursive.

Example:

Input - "2+3*4"
The operator of lowest precedence is +. After splitting at '+', you get "2" and "3*4".
"2" evaluates to 2, of course.
For "3*4", repeat the process.
   The lowest operator is *. After splitting at '*', you get "3" and "4".
   "3" is 3, "4" is 4.
   Since you split at '*', 3*4 = 12.
So "3*4" is 12.
Now, since you split at '+', 2+12 = 14

If you want (2+3)*4 work too, it's slightly harder. The idea is the same, but you need to ignore or remove ()s at times. Good luck.