Basic Compiler Design Gaming Project in C++

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3 months ago

#include <iostream>
#include <string>
#include <cctype>
#include <stdexcept>
#include <map>

using namespace std;

// Token types
enum class TokenType {
    NUMBER,
    PLUS,
    MINUS,
    MULTIPLY,
    DIVIDE,
    END,
    INVALID
};

// Token structure
struct Token {
    TokenType type;
    int value; // For NUMBER token
};

// Lexer class
class Lexer {
public:
    Lexer(const string& text) : text(text), pos(0), currentChar(text[pos]) {}

    Token getNextToken() {
        while (currentChar != '\0') {
            if (isspace(currentChar)) {
                skipWhitespace();
                continue;
            }

            if (isdigit(currentChar)) {
                return Token{TokenType::NUMBER, getNumber()};
            }

            if (currentChar == '+') {
                advance();
                return Token{TokenType::PLUS, 0};
            }

            if (currentChar == '-') {
                advance();
                return Token{TokenType::MINUS, 0};
            }

            if (currentChar == '*') {
                advance();
                return Token{TokenType::MULTIPLY, 0};
            }

            if (currentChar == '/') {
                advance();
                return Token{TokenType::DIVIDE, 0};
            }

            throw runtime_error("Invalid character");
        }

        return Token{TokenType::END, 0};
    }

private:
    string text;
    size_t pos;
    char currentChar;

    void advance() {
        ++pos;
        if (pos >= text.length()) {
            currentChar = '\0';
        } else {
            currentChar = text[pos];
        }
    }

    void skipWhitespace() {
        while (currentChar != '\0' && isspace(currentChar)) {
            advance();
        }
    }

    int getNumber() {
        string number;
        while (currentChar != '\0' && isdigit(currentChar)) {
            number += currentChar;
            advance();
        }
        return stoi(number);
    }
};

// Parser class
class Parser {
public:
    Parser(Lexer lexer) : lexer(lexer), currentToken(lexer.getNextToken()) {}

    int parse() {
        int result = expression();
        if (currentToken.type != TokenType::END) {
            throw runtime_error("Unexpected token after end of expression");
        }
        return result;
    }

private:
    Lexer lexer;
    Token currentToken;

    void eat(TokenType type) {
        if (currentToken.type == type) {
            currentToken = lexer.getNextToken();
        } else {
            throw runtime_error("Unexpected token type");
        }
    }

    int factor() {
        if (currentToken.type == TokenType::NUMBER) {
            int value = currentToken.value;
            eat(TokenType::NUMBER);
            return value;
        }
        throw runtime_error("Expected number");
    }

    int term() {
        int result = factor();
        while (currentToken.type == TokenType::MULTIPLY || currentToken.type == TokenType::DIVIDE) {
            TokenType op = currentToken.type;
            eat(op);
            if (op == TokenType::MULTIPLY) {
                result *= factor();
            } else {
                result /= factor();
            }
        }
        return result;
    }

    int expression() {
        int result = term();
        while (currentToken.type == TokenType::PLUS || currentToken.type == TokenType::MINUS) {
            TokenType op = currentToken.type;
            eat(op);
            if (op == TokenType::PLUS) {
                result += term();
            } else {
                result -= term();
            }
        }
        return result;
    }
};

int main() {
    string text;
    cout << "Enter an arithmetic expression: ";
    getline(cin, text);

    try {
        Lexer lexer(text);
        Parser parser(lexer);
        int result = parser.parse();
        cout << "Result: " << result << endl;
    } catch (const runtime_error& e) {
        cerr << "Error: " << e.what() << endl;
    }

    return 0;
}

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#include <iostream>

#include <string>

#include <cctype>

#include <stdexcept>

#include <map>

using namespace std;

// Token types

enum class TokenType {

NUMBER,

PLUS,

MINUS,

MULTIPLY,

DIVIDE,

END,

INVALID

};

// Token structure

struct Token {

TokenType type;

int value; // For NUMBER token

};

// Lexer class

class Lexer {

public:

Lexer(const string& text) : text(text), pos(0), currentChar(text[pos]) {}

Token getNextToken() {

while (currentChar != '\0') {

if (isspace(currentChar)) {

skipWhitespace();

continue;

}

if (isdigit(currentChar)) {

return Token{TokenType::NUMBER, getNumber()};

}

if (currentChar == '+') {

advance();

return Token{TokenType::PLUS, 0};

}

if (currentChar == '-') {

advance();

return Token{TokenType::MINUS, 0};

}

if (currentChar == '*') {

advance();

return Token{TokenType::MULTIPLY, 0};

}

if (currentChar == '/') {

advance();

return Token{TokenType::DIVIDE, 0};

}

throw runtime_error("Invalid character");

}

return Token{TokenType::END, 0};

}

private:

string text;

size_t pos;

char currentChar;

void advance() {

++pos;

if (pos >= text.length()) {

currentChar = '\0';

} else {

currentChar = text[pos];

}

void skipWhitespace() {

while (currentChar != '\0' && isspace(currentChar)) {

advance();

}

int getNumber() {

string number;

while (currentChar != '\0' && isdigit(currentChar)) {

number += currentChar;

advance();

}

return stoi(number);

}

};

// Parser class

class Parser {

public:

Parser(Lexer lexer) : lexer(lexer), currentToken(lexer.getNextToken()) {}

int parse() {

int result = expression();

if (currentToken.type != TokenType::END) {

throw runtime_error("Unexpected token after end of expression");

}

return result;

}

private:

Lexer lexer;

Token currentToken;

void eat(TokenType type) {

if (currentToken.type == type) {

currentToken = lexer.getNextToken();

} else {

throw runtime_error("Unexpected token type");

}

int factor() {

if (currentToken.type == TokenType::NUMBER) {

int value = currentToken.value;

eat(TokenType::NUMBER);

return value;

}

throw runtime_error("Expected number");

}

int term() {

int result = factor();

while (currentToken.type == TokenType::MULTIPLY || currentToken.type == TokenType::DIVIDE) {

TokenType op = currentToken.type;

eat(op);

if (op == TokenType::MULTIPLY) {

result *= factor();

} else {

result /= factor();

}

return result;

}

int expression() {

int result = term();

while (currentToken.type == TokenType::PLUS || currentToken.type == TokenType::MINUS) {

TokenType op = currentToken.type;

eat(op);

if (op == TokenType::PLUS) {

result += term();

} else {

result -= term();

}

return result;

}

};

int main() {

string text;

cout << "Enter an arithmetic expression: ";

getline(cin, text);

try {

Lexer lexer(text);

Parser parser(lexer);

int result = parser.parse();

cout << "Result: " << result << endl;

} catch (const runtime_error& e) {

cerr << "Error: " << e.what() << endl;

}

return 0;

}

Explanation

Token Types:
- TokenType is an enum class that defines different types of tokens: NUMBER
  
  Advertisement
  
  , PLUS, MINUS, MULTIPLY, DIVIDE, END, and INVALID.
Token Structure:
- Token holds the type of token and its value (if it’s a number).
Lexer Class:
- Purpose: Breaks the input text into tokens.
- Methods:
  - getNextToken(): Reads characters from the input and generates tokens. It handles numbers and arithmetic operators.
  - advance(): Moves to the next character in the input.
  - skipWhitespace(): Skips over whitespace characters.
  - getNumber(): Extracts multi-digit numbers from the input.
Parser Class:
- Purpose: Parses the tokens generated by the lexer and evaluates the arithmetic expression.
- Methods:
  - parse(): Starts the parsing process and returns the result.
  - eat(TokenType type): Consumes a token of the specified type.
  - factor(): Parses a number token.
  - term(): Handles multiplication and division operations.
  - expression(): Handles addition and subtraction operations.
Main Function (main):
- Reads an arithmetic expression from the user.
- Initializes the lexer and parser.
- Parses the expression and outputs the result.
- Handles errors gracefully using exception handling.

Explanation

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