詞法分析（編譯原理）

#include <iostream>
using namespace std;
#include <string.h>
char M[1000], Gjz[6][10] = {"begin", "if", "then", "while", "do", "end"};
void Set()
{
    char T[50];
    int i, j, now;
    i = now = 0;
    while (1)
    {
        switch (M[now])
        {
        case 'b':
            for (j = 0, i = now; i <= now + 4; i++, j++)
                T[j] = M[i];
            T[j] = '\0';
            if (strcmp(T, Gjz[0]) == 0)
            {
                cout << "(" << 1 << ","
                     << "begin"
                     << ")";
                now = i;
            }
            else
                goto loop;
            break;
        case 'i':
            for (j = 0, i = now; i <= now + 1; i++, j++)
                T[j] = M[i];
            T[j] = '\0';
            if (strcmp(T, Gjz[1]) == 0)
            {
                cout << "(" << 2 << ","
                     << "if"
                     << ")";
                now = i;
            }
            else
                goto loop;
            break;
        case 't':
            for (j = 0, i = now; i <= now + 3; i++, j++)
                T[j] = M[i];
            T[j] = '\0';
            if (strcmp(T, Gjz[2]) == 0)
            {
                cout << "(" << 3 << ","
                     << "then"
                     << ")";
                now = i;
            }
            else
                goto loop;
            break;
        case 'w':
            for (j = 0, i = now; i <= now + 4; i++, j++)
                T[j] = M[i];
            T[j] = '\0';
            if (strcmp(T, Gjz[3]) == 0)
            {
                cout << "(" << 4 << ","
                     << "while"
                     << ")";
                now = i;
            }
            else
                goto loop;
            break;
        case 'd':
            for (j = 0, i = now; i <= now + 1; i++, j++)
                T[j] = M[i];
            T[j] = '\0';
            if (strcmp(T, Gjz[4]) == 0)
            {
                cout << "(" << 5 << ","
                     << "do"
                     << ")";
                now = i;
            }
            else
                goto loop;
            break;
        case 'e':
            for (j = 0, i = now; i <= now + 2; i++, j++)
                T[j] = M[i];
            T[j] = '\0';
            if (strcmp(T, Gjz[5]) == 0)
            {
                cout << "(" << 6 << ","
                     << "end"
                     << ")";
                cout << "(" << 0 << "," << '#' << ")";
                exit(0);
            }
            else
                goto loop;
            break;
        case '+':
            cout << "(" << 13 << "," << '+' << ")";
            break;
        case '-':
            cout << "(" << 14 << "," << '-' << ")";
            break;
        case '*':
            cout << "(" << 15 << "," << '*' << ")";
            break;
        case '/':
            cout << "(" << 16 << "," << '/' << ")";
            break;
        case '=':
            cout << "(" << 25 << "," << '=' << ")";
            break;
        case ';':
            cout << "(" << 26 << "," << ';' << ")";
            break;
        case '(':
            cout << "(" << 27 << "," << '(' << ")";
            break;
        case ')':
            cout << "(" << 28 << "," << ')' << ")";
            break;
        case '<':
            if (M[now + 1] == '>')
            {
                cout << "(" << 21 << ","
                     << "<>"
                     << ")";
                now++;
            }
            else if (M[now + 1] == '=')
            {
                cout << "(" << 22 << ","
                     << "<="
                     << ")";
                now++;
            }
            else
                cout << "(" << 20 << ","
                     << "<"
                     << ")";
            break;
        case '>':
            if (M[now + 1] == '=')
            {
                cout << "(" << 24 << ","
                     << ">="
                     << ")";
                now++;
            }
            else
                cout << "(" << 23 << ","
                     << ">"
                     << ")";
            break;
        case ':':
            if (M[now + 1] == '=')
            {
                cout << "(" << 18 << ","
                     << ":="
                     << ")";
                now++;
            }
            else
                cout << "(" << 17 << ","
                     << ":"
                     << ")";
            break;
        }
    loop:
        if (((M[now] >= 'a' && M[now] <= 'z') || (M[now] >= 'A' && M[now] <= 'Z')))
        {
            i = 0;
            while ((M[now] >= 'a' && M[now] <= 'z') || (M[now] >= 'A' && M[now] <= 'Z') || (M[now] >= '0' && M[now] <= '9'))
            {
                T[i] = M[now];
                i++;
                now++;
            }
            T[i] = '\0';
            now--;
            cout << "(" << 10 << "," << T << ")";
        }
        else if (M[now] >= '0' && M[now] <= '9')
        {
            i = 0;
            while (M[now] >= '0' && M[now] <= '9') //和上一步判斷id10同樣，讓while浪費一步，保證指針的正常移動
            {
                T[i] = M[now];
                i++;
                now++;
            }
            T[i] = '\0';
            now--;
            cout << "(" << 11 << "," << T << ")";
        }
        now++;
    }
}
int main()
{
    int i = 0;
    cin >> M[i];
    while (M[i] != '#')
    {
        i++;
        cin >> M[i];
    }
    M[++i] = '\0';
    cout << M << endl;
    Set();
    return 0;
}