3.NFA

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

bool is_identifier(const char *token) {
    if (!isalpha(token[0]) && token[0] != '_')
        return false;
    for (int i = 1; token[i] != '\0'; i++) {
        if (!isalnum(token[i]) && token[i] != '_')
            return false;
    }
    return true;
}

bool is_constant(const char *token) {
    int i = 0, dot_count = 0;
    if (token[i] == '-' || token[i] == '+') i++;

    if (token[i] == '\0') return false;

    for (; token[i] != '\0'; i++) {
        if (token[i] == '.') {
            if (++dot_count > 1) return false;
        } else if (!isdigit(token[i])) {
            return false;
        }
    }
    return true;
}

bool is_operator(const char *token) {
    const char operators[] = {"+", "-", "", "/", "=", "==", "!=", "<", ">", "<=", ">="};
    for (int i = 0; i < sizeof(operators) / sizeof(operators[0]); i++) {
        if (strcmp(token, operators[i]) == 0)
            return true;
    }
    return false;
}

int main() {
    char token[100];
    printf("Enter a token: ");
    scanf("%s", token);

    if (is_operator(token))
        printf("Operator\n");
    else if (is_constant(token))
        printf("Constant\n");
    else if (is_identifier(token))
        printf("Identifier\n");
    else
        printf("Unknown\n");

    return 0;
}