Question

I am trying to understand the following code I found in a website so that I can use it for a project that evaluates boolean expressions. The code is below but I think it is in java because I do not understand it. Can you help me describe what it is doing in c++ so that I can understand it better?

The link to the code is here: https://stackoverflow.com/questions/16762057/algorithm-to-evaluate-value-of-boolean-expression
The code is below:

public static boolean evaluateBool(String s)
{
    Stack<Object> stack = new Stack<>();
    StringBuilder expression =new StringBuilder(s);
    expression.chars().forEach(ch->
    {
        if(ch=='0') stack.push(false);  
         else if(ch=='1') stack.push(true); 
          else if(ch=='A'||ch=='R'||ch=='X')
          {
              boolean op1 = (boolean) stack.pop();
              boolean op2 = (boolean) stack.pop();
              switch(ch)
              {
                case 'A' : stack.push(op2&&op1); break;
                case 'R' : stack.push(op2||op1); break;
                case 'X' : stack.push(op2^op1); break;
              }//endSwitch  
          }else 
              if(ch=='N')
                {
                  boolean op1 = (boolean) stack.pop();
                  stack.push(!op1);
                }//endIF
    });
    return (boolean) stack.pop();
}

Answer 1

public static boolean evaluateBool(String s)

{

Stack<Object> stack = new Stack<>();

//NOTE: it means that we are makeing a stack which is a object type, that means it can be string, int or any other type. lets we have a stack of string i.e "TF&|!()"

T

F

&

|

!

(

)

StringBuilder expression =new StringBuilder(s);

//NOTE: this will convert the stack in string i.e now the expression will be

expression ="TF&|!()" .

expression.chars().forEach(ch->

{

if(ch=='T') stack.push(false);  

else if(ch=='F') stack.push(true);

//NOTE: this will push the T and F in stack to execute the expression like:- ! ( T | F & F )

else if(ch=='&' || ch=='|' || ch=='!' )

{

boolean op1 = (boolean) stack.pop();

boolean op2 = (boolean) stack.pop();

//NOTE: this will POP the operator like:- &, | and ! from StringBuilder expression

switch(ch)

{

case '&' : stack.push(op2&&op1); break;

case '|' : stack.push(op2||op1); break;

case '!' : stack.push(op2^op1); break;

//NOTE: Most importantly,

these will convert the operatoe into real computer operators, as of now we have these operator in char. so '&' will be converted to && expression and '|' will be || and '!' will be converted into ^(NOt operator or bit operator)

}//endSwitch  

}else

if(ch=='(' || ch==')')

{

boolean op1 = (boolean) stack.pop();

stack.push(!op1);

}//endIF

});

return (boolean) stack.pop();

//NOTE: and at last when this stack is retured it is type casted into bool, so it will be like

! ( T | F & F )

and when it is in boolen form then the result will be returned i.e false.

}