Hello,

I need help in evaluating a boolean postfix expression.The EvaluateBooleanPostfixExpressionaccepts a string( that is already in postfix form) and it is supposed to evaluate it. I am stuck and need help in the evaluation part of the postfix expression where I am supposed to push the chars T and F into the stack and then pop the operators and then finally evaluate the expression. Thank you for your time and for your help in advance

The goal is to evaluate T and F expressions with AND(*), OR(+), and NOT(!). convert the input logical expression to postfix and then and then evaluate the expressions to evaluate the truth value of the logic expression now in postfix form.

(F+(!!F+(F)+!(T+T+!F+F+T)+F+F+F*T+F+F)+!F*F)*(!T+(T)) = F

T+!(T+T)*(T)*(!F)*T*T+!T+!T+F+T*!!F*!F*(F+!F*F)*F+F = T

(T*(!F*(F+T*!(F+T)+T*(!F*!!T+F*F))+F)+!(F+T)+F)*(T+!!F) = T

The code is below :

#include

#include

#include

#include

#include

#include

using namespace std;

//Function to return precedence of operators

int prec(char c)

{

if (c == '!')

return 3;

else if (c == '*')

return 2;

else if (c == '+')

return 1;

else

return -1;

}

string Postfix(string s)

{

std::stack st;

st.push('L');

int l = s.length();

string ns;

for (int i = 0; i < l; i++)

{

// If the scanned character is an operand, add it to output string.

if ((s[i] == 'T') || (s[i] == 'F'))

ns += s[i];

// If the scanned character is an (, push it to the stack.

else if (s[i] == '(')

st.push('(');

// If the scanned character is an ), pop and to output string from the stack

// until an ( is encountered.

else if (s[i] == ')')

{

while (st.top() != 'L' && st.top() != '(')

{

char c = st.top();

st.pop();

ns += c;

}

if (st.top() == '(')

{

char c = st.top();

st.pop();

}

}

//If an operator is scanned

else {

while (st.top() != 'L' && prec(s[i]) <= prec(st.top()))

{

char c = st.top();

st.pop();

ns += c;

}

st.push(s[i]);

}

}

//Pop all the remaining elements from the stack

while (st.top() != 'L')

{

char c = st.top();

st.pop();

ns += c;

}

cout << ns << endl;

return ns;

}

char EvaluateBooleanPostFixExpression(string x)

{

int n = x.length();

char Op1, char Op2, char symbol;

// create a stack the size of the string expression,

stackY;

/*

Evaluate the postfix expression here with the operators

Traverse all operands by jumping

a character after every iteration. (scan the characters)

*/

for (int i = 0; i < n; i += 2) {

// if a scanned character is an operand, push to the stack ( Operands are T or F)

if (IsOperand(n[i]))

{

// Extract the T or F from the string but keep incrementing i

// as long as they are T or F

}

// if the scanned character is an operator, then pop two elements from the stack and apply the operator

// the operators are + for OR, * for AND, ! for NOT

// the following parts evaluate the boolean expression

// If symbol next to current operand

// is AND.

if (symbol == '*') {

if (Op1 == 'F' || Op2 == 'F')

return 'F';

else

return 'T';

}

// If operator next to current operand

// is OR.

if (symbol == '+') {

if (Op1 == 'T' || Op2 == 'T')

return 'T';

else

return 'F';

}

if (symbol == '!')

{

if (Op1 == 'T')

return 'F';

else

return 'T';

}

}

}

bool IsOperand(char Operand)

{

if(Operand == 'T' && Operand == 'F')

return true;

else

return false;

}

bool IsOperator(char Operator)

{

if(Operator == '!' && Operator == '*' && Operator =='+')

return true;

else

return false;

}