编译原理：语法分析 词法分析简单C语言代码

#define _CRT_SECURE_NO_WARNINGS #include <stdio.h> #include <string.h> #include <stdlib.h> char string[50];//命令行读入的字符串 char get[10];//分析出来的关键字和标识符 int num;//种别码 int p;//当前词法分析正在进行的位置 char *keywords[6] = { "begin","if","then","while","do","end" }; //关键字数组 int n[20];//经词法分析得到的种别码的数组，语法分析时使用 int k;//词法分析的单词的总个数 int q=0;//当前语法分析正在进行的位置 //以下是语法分析的非终结符 bool S(); bool A(); bool B(); bool C(); bool D(); bool E(); bool F(); bool F1(); bool G(); bool G1(); void words(char ch) { int m = 0; int n; while (((ch <= 'z') && (ch >= 'a')) || ((ch <= 'Z') && (ch >= 'A')) || ((ch >= '0') && (ch <= '9'))) { get[m++] = ch; ch = string[p++]; } p--; num = 10; for (n = 0; n<6; n++) if (strcmp(get, keywords[n]) == 0) { num = n + 1; break; } get[m++] = '\0'; } int number(char ch) { int sum = 0; while ((ch >= '0') && (ch <= '9')) { sum = sum * 10 + ch - '0'; ch = string[p++]; } p--; num = 11; return sum; } void symbol(char ch) { int m = 0; switch (ch) { case '+':num = 13; get[m++] = ch; break; case '-':num = 14; get[m++] = ch; break; case '*': num = 15; get[m++] = ch; break; case '/': num = 16; get[m++] = ch; break; case ':': get[m++] = ch; ch = string[p++]; if (ch == '=') { num = 18; get[m++] = ch; } else { num = 17; p--; } break; case '<':get[m++] = ch; ch = string[p++]; if (ch == '=') { num = 22; get[m++] = ch; } else if (ch == '>') { num = 21; get[m++] = ch; } else { num = 20; p--; } break; case '>':get[m++] = ch; ch = string[p++]; if (ch == '=') { num = 24; get[m++] = ch; } else { num = 23; p--; } break; case '=': num = 25;get[m++] = ch;break; case ';': num = 26;get[m++] = ch;break; case '(': num = 27;get[m++] = ch;break; case ')': num = 28;get[m++] = ch;break; case '#': num = 0;get[m++] = ch;break; default: num = -1;break; } get[m++] = '\0'; } //语法分析 递归下降法************************************************** void lrparser() { if (S()) printf("Success!\n"); else printf("Error!\n"); } bool S() { if(n[k-1]!=6 && n[k - 2] != 26) { printf("error: 缺少 end\n");return false; } else if (n[k - 2] == 26) { printf("error: 缺少被赋值变量\n"); return false; } if (n[q] == 1) q++; else { printf("error: 缺少 begin\n");return false; } if (!A()) return false; if (n[q] == 6)return true; } bool A() { if (!B()) return false; if (!C()) return false; return true; } bool B() { if (n[q] == 10) q++; else return false; if (n[q] == 18) q++; else { printf("error: 缺少等号\n"); return false; } if (!E()) return false; return true; } bool C() { if (n[q] == 6) return true; if (n[q] == 26) q++; else { printf("error: 缺少 end \n"); return false; } if (!B()) return false; if (!D()) return false; return true; } bool D() { if (n[q] == 26 && C()) return true; if (n[q] == 6) return true; else { return false; printf("error: 缺少 end\n");} return false; } bool E() { if (!F()) return false; if (!F1()) return false; return true; } bool F1(){ if (n[q] == 26||n[q] == 6) return true; else if (n[q] == 13 || n[q] == 14) q++; if (!F()) return false; return true; } bool F() { if (!G()) return false; if (!G1()) return false; return true; } bool G1() { if (n[q] == 13 || n[q] == 14 || n[q] == 6 || n[q] == 26) return true; if (n[q] == 15 || n[q] == 16) q++; if (!G()) return false; return true; } bool G() { if (n[q] == 10) { q++; return true; } if (n[q] == 11) { q++; return true; } if (n[q] == 27) { q++; if (!E()) return false; else if(n[q]==28) { return true; q++; } } } //******************************************************* void main() { int i = 0; printf("请输入字符串，以#结束：\n\n"); char ch; do { scanf("%c", &ch); string[i++] = ch; } while (ch != '#'); p = 0; int sum, m;//数字的求和 //printf("\n词法分析二元组输出：\n"); do { memset(get, 0, sizeof(get));//清空get字符串 ch = string[p++]; m = 0; while ((ch == ' ') || (ch == '\n')) //对于代码中的空格和回车的处理 ch = string[p++]; if (((ch <= 'z') && (ch >= 'a')) || ((ch <= 'Z') && (ch >= 'A'))) words(ch);//对于代码中关键字和标识符的处理 else if ((ch >= '0') && (ch <= '9')) sum = number(ch);//对于代码中的数字的处理 else symbol(ch);//对于代码中的符号的处理 n[q] = num; q++; /*switch (num) { case 11:printf("( %-5d%5d )\n", sum, num); break; case -1:printf("出现一个错误的单词\n"); getchar(); exit(0); default: printf("( %-5s%5d )\n", get, num); break; }*/ } while (num != 0); k = q-1; q = 0; printf("\n语法分析结果如下：\n"); lrparser(); system("pause"); }