Prefix using stack

#include<iostream>
#include<stack>
using namespace std;

int EvaluatePrefix(string exp);
bool IsNumber(char ch);
bool IsOperator(char ch);
int PerformOperation(char ch, int op1, int op2);

int main()
{
	cout << "Prefix form: <operator> <operand> <operand>." << endl;
	string exp;
	cout << "\nEnter Prefix Expression: ";
	cin >> exp;
	int result = EvaluatePrefix(exp);
	cout << "\nResult = " << result << endl;

	return 0;
}
//
int EvaluatePrefix(string exp)
{
	stack<char> s;
	for (int i = exp.length(); i >= 0; i--)
	{
		if (IsNumber(exp[i]))
		{
			s.push(exp[i]-'0');
		}
		else if (IsOperator(exp[i]))
		{
			int op1 = s.top();    s.pop();
			int op2 = s.top();    s.pop();
			int result = PerformOperation(exp[i],op1,op2);
			s.push(result);
		}
	}
	return s.top();
}
//
bool IsNumber(char ch)
{
	if (ch >= '0' && ch <= '9')
		return true;
	return false;
}
//
bool IsOperator(char ch)
{
	if (ch == '+' || ch == '-' || ch == '*' || ch == '/')
		return true;
	return false;
}
//
int PerformOperation(char ch, int op1, int op2)
{
	if (ch == '+')             return op1 + op2;
	else if (ch == '-')        return op1 - op2;
	else if (ch == '*')        return op1 * op2;
	else if (ch == '/')        return op1 / op2;
	else                       return -1;
}

Source: codejudge.blogspot.com

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