编译原理头歌实验：词法分析程序设计与实现（C语言版）

1.实验描述

任务描述

本关任务：加深对词法分析器的工作过程的理解；加强对词法分析方法的掌握；能够采用一种编程语言实现简单的词法分析程序；能够使用自己编写的分析程序对简单的程序段进行词法分析。

编程要求

根据提示，在右侧编辑器补充代码标示符、数字符及其他字符符号的识别程序后，点击评测运行程序，系统会自动进行结果对比。

测试说明

平台会对你编写的代码进行测试：

测试输入：

using namespace std; int main() {
int year;
cout << “hello” << endl;
return 0; }

2.实验操作提示

2.1定义目标语言的可用符号表和构词规则。

我们需要对五种单词符号进行识别分析，这里将单词符号分为三大块进行识别。首先判断字符是否为关键字或者标识符，并与已定义好的关键字进行比较，从而判断为关键字或者标识符；然后是数字的识别；最后是其他字符的判断，它们被一一定义好的判断进行识别，这样所有的字符便被识别出来了。标示符和关键字的判断

if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z'))  //可能是标示符或者关键字

字符与关键字的区别通过对比得出：

if (strcmp(token, rwtab1[n]) == 0){syn = 2;break;}else if (strcmp(token, rwtab[n]) == 0) {syn = 1;break;}}

对于数字的识别：

else if ((ch >= '0' && ch <= '9'))  //数字

其他字符的识别，他们被一一定义进行识别：

else switch (ch)   //其他字符 {case'<':m = 0; token[m++] = ch;ch = prog[p++];if (ch == '>'){syn = 4;token[m++] = ch;}else if (ch == '='){syn = 4;token[m++] = ch;}else{syn = 4;p--;}break;case'>':m = 0; token[m++] = ch;ch = prog[p++];if (ch == '='){syn = 4;token[m++] = ch;}else{syn = 4;p--;}break;case':':m = 0; token[m++] = ch;ch = prog[p++];if (ch == '='){syn = 4;token[m++] = ch;}else{syn = 4;p--;}break;case'*':syn = 4; token[0] = ch; break;case'/':syn = 4; token[0] = ch; break;case'+':syn = 4; token[0] = ch; break;case'-':syn = 4; token[0] = ch; break;case'=':syn = 4; token[0] = ch; break;case';':syn = 5; token[0] = ch; break;case',':syn = 5; token[0] = ch; break;case'(':syn = 5; token[0] = ch; break;case')':syn = 5; token[0] = ch; break;case'{':syn = 5; token[0] = ch; break;case'}':syn = 5; token[0] = ch; break;case'#':syn = 0; token[0] = ch; break;case'\n':syn = -2; break;default: syn = -1; break;}
}

依次读入源程序符号，对源程序进行单词切分和识别，直到源程序结束。
字符的输入我们使用cin.get() 获取，并切分保存在 prog中：

p = 0;row = 1;cout << "Please input string:" << endl;do{cin.get(ch);prog[p++] = ch;} while (ch != '#');p = 0;

对正确的单词，按照它的种别以<种别码，值>的形式保存在符号表中；

对不正确的单词，做出错误处理。
单词识别后，我们对返回的符号按3，4的规则进行输出：

{scaner();switch (syn){case 0: break;case 3: cout << "(" << syn << "," << sum << ")" << endl; break;case -1: cout << "Error in row " << row << "!" << endl; break;case -2: row = row++; break;default: cout << "(" << syn << "," << token << ")" << endl; break;}} while (syn != 0);

3.实验代码展示

#include <stdio.h>
#include <string.h>
#include <iostream>
using namespace std;
char prog[1000], token[20];
char ch;
int syn, p, m = 0, n, row = 1, sum = 0;
// 扩充关键字表
const char* rwtab[10] = { "if","int","for","while","do","return","break","continue", "using", "namespace" };
const char* rwtab1[8] = { "main","a","b","c","d","e","f","g" };void scaner()
{// 初始化token数组for (n = 0; n < 20; n++) token[n] = '\0';// 跳过空白字符while (p < strlen(prog) && (prog[p] == ' ' || prog[p] == '\t' || prog[p] == '\n')){if (prog[p] == '\n')row++;p++;}if (p >= strlen(prog)){syn = 0;return;}ch = prog[p++];// 进行标示符或者关键字的识别if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z')){m = 0;while ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || (ch >= '0' && ch <= '9')){token[m++] = ch;if (p >= strlen(prog))break;ch = prog[p++];}token[m] = '\0';if (p < strlen(prog))p--;syn = 2;for (n = 0; n < 10; n++) // 更新关键字表长度{if (strcmp(token, rwtab[n]) == 0){syn = 1;break;}}}// 进行数字的识别else if (ch >= '0' && ch <= '9'){sum = 0;while (ch >= '0' && ch <= '9'){sum = sum * 10 + (ch - '0');if (p >= strlen(prog))break;ch = prog[p++];}if (p < strlen(prog))p--;syn = 3;}// 进行其他字符的识别else{switch (ch){case '<':m = 0;token[m++] = ch;if (p < strlen(prog) && prog[p] == '<'){token[m++] = prog[p++];syn = 4;}else{syn = 4;p--;}break;case '>':m = 0;token[m++] = ch;if (p < strlen(prog) && prog[p] == '='){token[m++] = prog[p++];syn = 4;}else{syn = 4;p--;}break;case ':':m = 0;token[m++] = ch;if (p < strlen(prog) && prog[p] == '='){token[m++] = prog[p++];syn = 4;}else{syn = 4;p--;}break;case '*':syn = 4;token[0] = ch;break;case '/':syn = 4;token[0] = ch;if (p < strlen(prog) && prog[p] == '/') {token[1] = '/';syn = 5; // 注释符号作为界符处理p++;}break;case '+':syn = 4;token[0] = ch;break;case '-':syn = 4;token[0] = ch;break;case '=':syn = 4;token[0] = ch;break;case ';':syn = 5;token[0] = ch;break;case ',':syn = 5;token[0] = ch;break;case '(':syn = 5;token[0] = ch;break;case ')':syn = 5;token[0] = ch;break;case '{':syn = 5;token[0] = ch;break;case '}':syn = 5;token[0] = ch;break;case '#':syn = 0;token[0] = ch;break;case '"':syn = 5;token[0] = ch;break;default:syn = -1;break;}}
}int main()
{// 输入p = 0;cout << "Please input string:" << endl;do{cin.get(ch);prog[p++] = ch;} while (ch != '#');prog[p] = '\0';p = 0;// 输出do{scaner();switch (syn){case 0:break;case 3:cout << "(" << syn << "," << sum << ")" << endl;break;case -1:cout << "Error in row " << row << "!" << endl;break;default:cout << "(" << syn << "," << token << ")" << endl;break;}} while (syn != 0);return 0;
}