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Programming Methodology

Implement a Stack to Evaluate Logical Expressions in C++

In this C++ exercise, you will implement a stack to evaluate logical expressions. The logical expressions will use operators like AND (&&), OR (||), and NOT (!). The program will read the expression, evaluate the logical operations using a stack, and return the result. The exercise aims to teach you how to manipulate a stack data structure to evaluate complex expressions while understanding logical operators' behavior. The stack will be used to store intermediate results and operators during the evaluation process.

Group

Data Structures: Stacks, Queues in C++

Objective

1. Implement a stack to hold values (either true or false) during evaluation.
2. Read a logical expression containing operators: AND (&&), OR (||), and NOT (!).
3. Use the stack to evaluate the expression by processing the operands and operators one by one.
4. After processing all operators and operands, output the final result as true or false.
5. Handle basic logical expressions with proper operator precedence.

Implement a stack to evaluate logical expressions.

Example C++ Exercise

 Copy C++ Code 
#include <iostream>  // Include for input/output operations
#include <stack>     // Include for stack operations
#include <string>    // Include for string manipulations
#include <sstream>   // Include for stringstream operations

using namespace std;

// Function to evaluate logical expressions
bool evaluateLogicalExpression(string expr) {
    stack s;  // Stack to store boolean values (true/false)
    stringstream ss(expr);  // Stringstream to process the expression
    string token;  // To store individual tokens (operand or operator)

    // Process each token in the expression
    while (ss >> token) {
        if (token == "true") {
            s.push(true);  // Push true onto the stack
        } else if (token == "false") {
            s.push(false);  // Push false onto the stack
        } else if (token == "&&") {
            bool b2 = s.top(); s.pop();  // Pop the second operand
            bool b1 = s.top(); s.pop();  // Pop the first operand
            s.push(b1 && b2);  // Perform AND operation and push the result
        } else if (token == "||") {
            bool b2 = s.top(); s.pop();  // Pop the second operand
            bool b1 = s.top(); s.pop();  // Pop the first operand
            s.push(b1 || b2);  // Perform OR operation and push the result
        } else if (token == "!") {
            bool b = s.top(); s.pop();  // Pop the operand
            s.push(!b);  // Perform NOT operation and push the result
        }
    }

    // Return the final result (the top element of the stack)
    return s.top();
}

// Main function to test the logical expression evaluation
int main() {
    string expr = "true false && true || ! false &&";  // Example logical expression

    // Evaluate the expression
    bool result = evaluateLogicalExpression(expr);

    // Output the result
    cout << "Result of the logical expression: " << (result ? "true" : "false") << endl;

    return 0;
}

 Output

Result of the logical expression: true

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