// This program evaluates simple expressions
//   number1 operator1 number2 operator2 number3
//   e.g., 3 + 4 * 5
// the program computes the answer using C++
// precedence, i.e., * comes before +.
// For this simple example, we will just use
// the operators *, +, /, -.
//
//

#include <iostream>
int main()
{
	double n1, n2, n3;
	double result;
	char op1, op2;
	int op1_priority, op2_priority;

	cout << "Enter an expression: ";
	cin >> n1 >> op1 >> n2 >> op2 >> n3;

	// decide whether op1 has higher precedence than op2

	op1_priority = 1;
    if (op1 == '+' || op1 == '-')
		op1_priority = 2;

	op2_priority = 1;
    if (op2 == '+' || op2 == '-')
		op2_priority = 2;


	// if op2 has higher priority than op1
	if (op2_priority < op1_priority)
	{
		// first evaluate op2, then evaluate op1
		if (op2 == '+')
			result = n2 + n3;
		else if (op2 == '*')
			result = n2 * n3;
		else if (op2 == '-')
			result = n2 - n3;
		else if (op2 == '/')
			result = n2 / n3;

		if (op1 == '+')
			result = n1 + result;
		else if (op1 == '*')
			result = n1 * result;
		else if (op1 == '-')
			result = n1 - result;
		else if (op1 == '/')
			result = n1 / result;
	}
	else
	{
		// first evaluate op1, then evaluate op2

		// here is a way to do this first step for op1
		// using if / else if / else construct
		//
		//if (op1 == '+')
		//    result = n1 + n2;
		//else if (op1 == '*')
		//    result = n1 * n2;
		//else if (op1 == '-')
		//    result = n1 - n2;
		//else if (op1 == '/')
		//    result = n1 / n2;
		//else
		//    cout << "ERROR: op1 is invalid\n";

		// here is a way to do the same thing using a switch statement
		switch (op1)
		{
			case '+':
				result = n1 + n2;
				break;
		    case '*':
				result = n1 * n2;
				break;
		    case '-':
				result = n1 - n2;
				break;
		    case '/':
				result = n1 / n2;
				break;
		    default:
				cout << "ERROR: op1 is invalid\n";
		}

		if (op2 == '+')
			result = result + n3;
		if (op2 == '*')
			result = result * n3;
		if (op2 == '-')
			result = result - n3;
		if (op2 == '/')
			result = result / n3;
	}
	
	cout << "The answer is " << result << endl;
}