cpp/16_PrefixExpressionEvaluation.cpp at master · priyanshu1044/cpp · GitHub

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#include <bits/stdc++.h>
using namespace std;
int prefixEvaluation(string s)
{
    stack<int> st;
    for (int i = s.length()-1; i >= 0; i--)
    {
        if (s[i] >= '0' && s[i] <= '9')
        {
            st.push(s[i] - '0');
        }
        else
        {
            int op1 = st.top();
            st.pop();
            int op2 = st.top();
            st.pop();

            switch (s[i])
            {
            case '+':
                st.push(op1 + op2);
                break;

            case '-':
                st.push(op1 - op2);
                break;

            case '*':
                st.push(op1 * op2);
                break;

            case '/':
                st.push(op1 / op2);
                break;

            case '^':
                st.push(pow(op1, op2));
                break;
            }
        }
    }
    return st.top();
}
int main()
{
    cout << prefixEvaluation("-+7*45+20") << endl;
    return 0;
}