Postfix Exp
I am having a problem with my postfix algorithm
Right off the bat, when I ask the user to enter a postfix expression such as: ab*
the program will say the size of this string is 2, not 3, which is already causing all sorts of problems
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#include <iostream>
#include <string>
#include <stack>
using namespace std;
int eval(int var1, int var2, char ops);
int main()
{
string exp;
int *vars;
int var1, var2;
int result = 0;
char op;
stack<char> ops;
cout << "Please enter a postfix expression" << endl;
cin.ignore();
getline(cin, exp);
cout << exp.length();
if (exp.length() >= 3)
{
//calculate how many expressions
vars = new int[exp.length()];
int counter = 0;
while (counter != exp.length() - 1)
{
if (exp[counter] >= 65 && exp[counter] <= 90)
{
counter++;
cout << "Enter a value for: " << exp[counter] << ":" << endl;
cin >> vars[counter];
}
else if (exp[counter] == '+' || exp[counter] == '-' || exp[counter] == '*' || exp[counter] == '/')
{
vars[counter] = '0'; //add a 0 to variable slot
counter++;
ops.push(exp[counter]); //pushes operator
var1 = counter - 2; //the last 2 variables
var2 = counter - 1; //the previous variable
op = ops.top();
ops.pop();
result = eval(var1, var2, op);
}
}
}
else if (exp.length() < 3)
{
cout << "Not a complete expression!" << endl;
}
cout << "The result of the expression is: " << result << endl;
system("PAUSE");
return 0;
}
int eval(int var1, int var2, char ops)
{
switch (ops)
{
case '+': return var1 + var2;
case '*': return var1*var2;
case '/': return var1 / var2;
case'-': return var1 - var2;
default: return 0;
}
}
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You need to remove this cin.ignore () on line 18
Even when I remove cin.ignore(), it still says the size of the string is 2, when it should be 3... it's like it doesn't count "*" or "+" as chars
It works for me
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#include <iostream>
#include <string>
using namespace std;
int main()
{
string expr;
cout << "Enter expression: ";
getline(cin, expr);
cout << "\nYour input: " << expr << "\n\nLength of expr: " << expr.length() << "\n";
cout << "\nSize of expr: " << expr.size() << "\n\n";
system("pause");
return 0;
}
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