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  1. #include <cctype>
  2. #include <cmath>
  3. #include <cstdlib>
  4. #include <cstring>
  5. #include <iostream>
  6. #include <sstream>
  7. #include <stack>
  8. #include <stdio.h>
  9.  
  10. using namespace std;
  11.  
  12. class DividedByZero : public exception {};
  13.  
  14. bool is_balanced(const string &parenthesis) // for checking parentheses
  15. {
  16.     stack<char> store;
  17.     char check;
  18.     for (string::size_type i = 0; i < parenthesis.length(); ++i) {
  19.         check = parenthesis[i];
  20.         if (check == '(' || check == '{' || check == '[') { store.push(check); }
  21.         if (!store.empty()) {
  22.             if (check == ')') {
  23.                 if (store.top() == '(') {
  24.                     store.pop();
  25.                     continue;
  26.                 } else {
  27.                     break;
  28.                 }
  29.             }
  30.             if (check == '}') {
  31.                 if (store.top() == '{') {
  32.                     store.pop();
  33.                     continue;
  34.                 } else {
  35.                     break;
  36.                 }
  37.             }
  38.             if (check == ']') {
  39.                 if (store.top() == '[') {
  40.                     store.pop();
  41.                     continue;
  42.                 } else {
  43.                     break;
  44.                 }
  45.             }
  46.         } else
  47.             break;
  48.     }
  49.     return (store.empty());
  50. }
  51.  
  52. double precedence(char op) // precedence rules of operators
  53. {
  54.     if (op == '+' || op == '-')
  55.         return 1;
  56.     else if (op == '*' || op == '/')
  57.         return 2;
  58.     return 0;
  59. }
  60.  
  61. void parse_stack_top(stack<double> &operand, stack<char> &operation) // parse stack top
  62. {
  63.     double number1, number2;
  64.  
  65.     number2 = operand.top();
  66.     operand.pop();
  67.  
  68.     number1 = operand.top();
  69.     operand.pop();
  70.  
  71.     switch (operation.top()) {
  72.     case '+': operand.push(number1 + number2); break;
  73.  
  74.     case '-': operand.push(number1 - number2); break;
  75.  
  76.     case '*': operand.push(number1 * number2); break;
  77.  
  78.     case '/':
  79.         if (number2 == 0) // if number2 = 0, can not devide by zero
  80.         {
  81.             cout << "\nError!: Divide by zero.";
  82.             throw DividedByZero();
  83.         } else
  84.             operand.push(number1 / number2);
  85.     }
  86.     operation.pop();
  87. }
  88.  
  89. double evaluate_stack(const string &token) // evaluate expression
  90. {
  91.     stack<double> operand;
  92.     stack<char> operation;
  93.  
  94.     for (string::size_type i = 0; i < token.size(); i++) {
  95.         if (isdigit(token[i]) || token[i] == '.') // check for numberic, and double value
  96.         {
  97.             double val = 0;
  98.             while (i < token.size() && isdigit(token[i])) // if element of number is larger than one
  99.             {
  100.                 val = (val * 10) + (token[i] - '0');
  101.                 i++;
  102.             }
  103.             if (token[i] == '.') {
  104.                 double resp = 0;
  105.                 i++;
  106.                 int powTen = 10;
  107.                 while (i < token.size() && isdigit(token[i])) {
  108.                     resp = resp + double(token[i] - '0') / powTen;
  109.                     powTen *= 10;
  110.                     i++;
  111.                 }
  112.                 val += resp;
  113.             }
  114.             if (!isdigit(token[i])) i--;
  115.             operand.push(val);
  116.         } else if (token[i] == '+' || token[i] == '-' || token[i] == '*' || token[i] == '/') {
  117.             while (!operation.empty() &&  precedence(token[i]) < precedence(operation.top())) {
  118.                 parse_stack_top(operand, operation);
  119.             }
  120.             operation.push(token[i]);
  121.         } else if (token[i] == '(' || token[i] == '{' || token[i] == '[') {
  122.             operation.push('(');
  123.         }
  124.  
  125.         else if (token[i] == ')' || token[i] == '}' || token[i] == ']') {
  126.             while (!operation.empty() && operation.top() != '(') {
  127.                 parse_stack_top(operand, operation);
  128.             }
  129.             operation.pop();
  130.         }
  131.     }
  132.     while (!operation.empty()) { parse_stack_top(operand, operation); }
  133.     return operand.top();
  134. }
  135.  
  136. int main(int argc, char **argv) {
  137.  
  138.     string token;
  139.  
  140.     cout << "\nYour Expression: ";
  141.     getline(cin, token);
  142.  
  143.     if (is_balanced(token)) {
  144.         cout << "\nResult: " << evaluate_stack(token);
  145.  
  146.     } else
  147.         cout << "\nError!: parentheses is not balanced!";
  148.  
  149.  
  150.     return 0;
  151. }
Success #stdin #stdout 0s 4248KB
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stdin
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{10.1+8.4*4.8}/2.2
stdout
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Your Expression: 
Result: 22.9182
https://ideone.com/QmF4rV
Calculator
language:
C++ (gcc 8.3)
created:
6 years ago
visibility:
secret

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