122 lines
3.1 KiB
C++
122 lines
3.1 KiB
C++
#include <iostream>
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#include <stack>
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#include <string>
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#include <cctype>
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#include <map>
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// Function to convert infix expression to postfix expression
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std::string infixToPostfix(const std::string &infix)
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{
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std::stack<char> s;
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std::string postfix;
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std::map<char, int> precedence = {{'+', 1}, {'-', 1}, {'*', 2}, {'/', 2}, {'(', 0}};
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for (char c : infix)
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{
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if (std::isalnum(c))
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{ // 1. if operand, add to postfix
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postfix += c;
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}
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else if (c == '(')
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{ // 2. if '(', push to stack
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s.push(c);
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}
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else if (c == ')')
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{ // 3. if ')', pop until '('
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while (!s.empty() && s.top() != '(')
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{
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postfix += s.top();
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s.pop();
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}
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if (!s.empty())
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s.pop(); // pop '('
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}
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else
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{ // 4. if operator, pop operators with greater or equal precedence
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while (!s.empty() && precedence[c] <= precedence[s.top()])
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{
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postfix += s.top();
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s.pop();
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}
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s.push(c); // push current operator
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}
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}
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// 5. pop remaining operators
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while (!s.empty())
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{
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postfix += s.top();
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s.pop();
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}
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return postfix;
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}
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// Function to evaluate postfix expression
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int evaluatePostfix(const std::string &postfix)
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{
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std::stack<int> s;
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for (char c : postfix)
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{
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if (std::isdigit(c))
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{ // 1. if operand, push to stack
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s.push(c - '0');
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}
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else
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{ // 2. if operator, pop two operands, evaluate and push result
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int op2 = s.top();
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s.pop();
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int op1 = s.top();
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s.pop();
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switch (c)
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{
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case '+':
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s.push(op1 + op2);
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break;
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case '-':
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s.push(op1 - op2);
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break;
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case '*':
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s.push(op1 * op2);
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break;
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case '/':
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s.push(op1 / op2);
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break;
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}
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}
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}
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return s.top(); // 3. result is the only element in stack
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}
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int main()
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{
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std::string infix;
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// std::cout << "Enter an arithmetic expression: ";
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// std::getline(std::cin, infix);
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std::cout << "e.g. 1 1+4*5" << std::endl;
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infix = "1+4*5";
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std::string postfix = infixToPostfix(infix);
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std::cout << "Postfix expression: " << postfix << std::endl;
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int result = evaluatePostfix(postfix);
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std::cout << "Result: " << result << std::endl;
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std::cout << "e.g. 2 (1+4)*5" << std::endl;
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infix = "(1+4)*5";
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postfix = infixToPostfix(infix);
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std::cout << "Postfix expression: " << postfix << std::endl;
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result = evaluatePostfix(postfix);
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std::cout << "Result: " << result << std::endl;
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std::cout << "e.g. 3 1+4-5" << std::endl;
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infix = "1+4-5";
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postfix = infixToPostfix(infix);
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std::cout << "Postfix expression: " << postfix << std::endl;
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result = evaluatePostfix(postfix);
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std::cout << "Result: " << result << std::endl;
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return 0;
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}
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