compiler design homework - parser

parser.c

#include <stdio.h>
#include <ctype.h>

char currentToken;

void getToken() {
    currentToken = getchar();
}

int P();
int C();
int I();
int W();
int A();
int Ç();
int G();
int E();
int T();
int U();
int F();
int K();
int R();

int main() {
    // Set the initial value of n to 0
    int n = 0;

    // Read the input string
    printf("Enter the input string: ");
    getToken();

    // Call the P() function to parse and verify the input
    if (P()) {
        printf("Input is valid.\n");
    } else {
        printf("Input is invalid.\n");
    }

    return 0;
}




// P → {C} '.'
int P() {
    while (C()) {}
    if (currentToken == '.') {
        getToken();
        return 1;
    }
    return 0;
}

// C → I | W | A | Ç | G
int C() {
    if (I() || W() || A() || Ç() || G()) {
        return 1;
    }
    return 0;
}

// I → '[' E '?' C{ C } ':' C{ C } ']' | '[' E '?' C{C} ']'
int I() {
    if (currentToken == '[') {
        getToken();
        if (E() && currentToken == '?') {
            getToken();
            while (C()) {}
            if (currentToken == ':') {
                getToken();
                while (C()) {}
            }
            if (currentToken == ']') {
                getToken();
                return 1;
            }
        }
    }
    return 0;
}

// W → '{' E '?' C{C} '}'
int W() {
    if (currentToken == '{') {
        getToken();
        if (E() && currentToken == '?') {
            getToken();
            while (C()) {}
            if (currentToken == '}') {
                getToken();
                return 1;
            }
        }
    }
    return 0;
}

// A → K '=' E ';'
int A() {
    if (K() && currentToken == '=') {
        getToken();
        if (E() && currentToken == ';') {
            getToken();
            return 1;
        }
    }
    return 0;
}

// Ç → '<' E ';'
int Ç() {
    if (currentToken == '<') {
        getToken();
        if (E() && currentToken == ';') {
            getToken();
            return 1;
        }
    }
    return 0;
}

// G → '>' K ';'
int G() {
    if (currentToken == '>') {
        getToken();
        if (K() && currentToken == ';') {
            getToken();
            return 1;
        }
    }
    return 0;
}

// E → T {('+' | '-') T}
int E() {
    if (T()) {
        while (currentToken == '+' || currentToken == '-') {
            getToken();
            if (!T()) {
                return 0;
            }
        }
        return 1;
    }
    return 0;
}

// T → U {('*' | '/' | '%') U}
int T() {
    if (U()) {
        while (currentToken == '*' || currentToken == '/' || currentToken == '%') {
            getToken();
            if (!U()) {
                return 0;
            }
        }
        return 1;
    }
    return 0;
}

// U → F '^' U | F
int U() {
    if (F()) {
        if (currentToken == '^') {
            getToken();
            if (!U()) {
                return 0;
            }
        }
        return 1;
    }
    return 0;
}

// F → '(' E ')' | K | R
int F() {
    if (currentToken == '(') {
        getToken();
        if (E() && currentToken == ')') {
            getToken();
            return 1;
        }
    } else if (K() || R()) {
        return 1;
    }
    return 0;
}

// K → 'a' | 'b' | ... | 'z'
int K() {
    if (islower(currentToken)) {
        getToken();
        return 1;
    }
    return 0;
}

// R → '0' | '1' | ... | '9'
int R() {
    if (isdigit(currentToken)) {
        getToken();
        return 1;
    }
    return 0;
}