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  1. #include<iostream>
  2. #include<stack>
  3. using namespace std;
  4.  
  5. bool evaluate(const char *expression, int &result);
  6. int calculate( int value1, int value2, char operation);
  7. int main()
  8. {
  9.     int result = 0;
  10.     char input[100];
  11.     cout<<"Enter an algebraic expression to evaluate ";
  12.     cin>>input;
  13.  
  14.     if (evaluate(input,result))
  15.         cout<<endl<<"The value of the evaluated expression is "<< result;
  16.     else
  17.         cout<<endl<<"Please enter a valid expression to evaluate";
  18. }
  19.  
  20. bool evaluate(const char *expression, int &result)
  21. {
  22.     stack<int> operands;
  23.     stack<char> operators;
  24.  
  25.     while(*expression != '\0')
  26.     {
  27.         if(*expression == ' ')
  28.         {
  29.             *expression++;
  30.             continue;
  31.         }
  32.  
  33.         else if(isdigit(*expression))
  34.         {
  35.             int number = 0;
  36.             while(isdigit(*expression))
  37.             {
  38.                number = number *10 + (*expression - '0') ;
  39.                *expression++;
  40.             }
  41.             operands.push(number);
  42.         }
  43.  
  44.         else if(*expression == '(')
  45.         {
  46.             operators.push(*expression);
  47.         }
  48.  
  49.         else if(*expression == '+' || *expression == '-' || *expression == '*' || *expression == '/')
  50.         {
  51.             operators.push(*expression);
  52.         }
  53.  
  54.         else if(*expression == ')')
  55.         {
  56.              while(!operators.empty() && operators.top() != '(')
  57.             {
  58.                 int value2 = operands.top();
  59.                 operands.pop();
  60.                 int value1 = operands.top();
  61.                 operands.pop();
  62.                 char op = operators.top();
  63.                 operators.pop();
  64.                 operands.push(calculate(value1, value2, op));
  65.             }
  66.             if(!operators.empty())
  67.                operators.pop();
  68.         }
  69.  
  70.         else
  71.         {
  72.             return(false);
  73.         }
  74. *expression++;
  75.     }
  76.  
  77.     while(operands.size()!= 0)
  78.     {
  79.         int value2 = operands.top();
  80.         operands.pop();
  81.         int value1 = operands.top();
  82.         operands.pop();
  83.         char op = operators.top();
  84.         operators.pop();
  85.         operands.push(calculate(value1, value2, op));
  86.     }
  87. return(true);
  88. }
  89.  
  90. int calculate( int value1, int value2, char operation)
  91. {
  92.       switch(operation){
  93.         case '+': return value1 + value2;
  94.         case '-': return value1 - value2;
  95.         case '*': return value1 * value2;
  96.         case '/': return value1 / value2;
  97. }
  98. }
  99.  
Success #stdin #stdout 0s 4364KB
comments (?)
stdin
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Standard input is empty
stdout
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Enter an algebraic expression to evaluate 
Please enter a valid expression to evaluate
https://ideone.com/7hNUGy
language:
C++ (gcc 8.3)
created:
4 years ago
visibility:
public

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