词法分析程序（Lexical Analyzer）要求：
- 从左至右扫描构成源程序的字符流
- 识别出有词法意义的单词（Lexemes）
- 返回单词记录（单词类别，单词本身）
- 滤掉空格
- 跳过注释
- 发现词法错误
程序结构：
输入：字符流（什么输入方式，什么数据结构保存）
处理：
–遍历（什么遍历方式）
–词法规则
输出：单词流（什么输出形式）
–二元组
单词类别：
1.标识符（10）
2.无符号数（11）
3.保留字（一词一码）
4.运算符（一词一码）
5.界符（一词一码）
|
单词符号 |
种别码 |
单词符号 |
种别码 |
|
begin |
1 |
: |
17 |
|
if |
2 |
:= |
18 |
|
then |
3 |
< |
20 |
|
while |
4 |
<= |
21 |
|
do |
5 |
<> |
22 |
|
end |
6 |
> |
23 |
|
l(l|d)* |
10 |
>= |
24 |
|
dd* |
11 |
= |
25 |
|
+ |
13 |
; |
26 |
|
- |
14 |
( |
27 |
|
* |
15 |
) |
28 |
|
/ |
16 |
# |
0 |
1 #include<stdio.h>
2 #include<string.h>
3 #include<stdlib.h>
4 char savearray[100],outarray[100];
5 char ch;
6 int row,arrays,count,m,i,p;//count为计数器 p为指针
7 char *wordsymbol[6] = {"if", "begin", "then", "while", "do", "end"};
8 void getarrays(){
9 for(i = 0; i < 8; i++){
10 outarray[i] == NULL;
11 }
12 ch = savearray[p++];
13 while(ch == ' '){
14 ch = savearray[p];
15 p++;
16 }
17
18 if((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <='Z')){
19 m = 0;
20 while((ch <= '9' && ch>= '0') || (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z')){
21 outarray[m++] = ch;
22 ch = savearray[p++];
23 }
24 outarray[m++] = '\0';
25 p--;
26 arrays = 10;
27 for(i = 0; i < 6; i++){
28 if(strcmp(wordsymbol[i],outarray) == 0){
29 arrays =1 + i;
30 break;
31 }
32
33 }
34 }else if(ch <= '9' && ch>= '0'){
35 count = 0;
36 while(ch >= '0' && ch <='9'){
37 count *= 10 + (ch - '0');
38 ch = savearray[p++];
39 }
40 p--;
41 arrays = 11;
42 } else switch(ch){
43 case '+':
44 outarray[0] = ch;
45 arrays = 13;
46 return;
47 case '-':
48 outarray[0] = ch;
49 arrays = 14;
50 return;
51 case '*':
52 outarray[0] = ch;
53 arrays = 15;
54 break;
55 case '/':
56 outarray[0] = ch;
57 arrays = 16;
58 break;
59 case ':':
60 i = 0;
61 outarray[i++] = ch;
62 ch = savearray[p++];
63 if(ch == '='){
64 outarray[i++] = ch;
65 arrays = 18;
66 }else{
67 arrays = 17;
68 p--;
69 }
70 return;
71
72 case '<':
73 i = 0;
74 outarray[i++] = ch;
75 ch = savearray[p++];
76 if(ch == '='){
77 outarray[i++] = ch;
78 arrays = 21;
79
80 }else if(ch == '='){
81 outarray[i++] = ch;
82 arrays = 22;
83 }else{
84 arrays = 20;
85 p--;
86 }
87 return;
88 case '>':
89 i = 0;
90 outarray[i++] = ch;
91 ch = savearray[p++];
92 if(ch == '='){
93 outarray[i++] = ch;
94 arrays = 24;
95 }else{
96 arrays = 23;
97 p--;
98 }
99 return;
100 case '=':
101 outarray[0] = ch;
102 arrays = 25;
103 break;
104 case ';':
105 outarray[0] = ch;
106 arrays = 26;
107 break;
108 case '(':
109 outarray[0] = ch;
110 arrays = 27;
111 break;
112 case ')':
113 outarray[0] = ch;
114 arrays = 28;
115 break;
116 case '#':
117 outarray[0] = ch;
118 arrays = 0;
119 break;
120 case '\n':
121 arrays = 100;
122 break;
123 default:
124 arrays = -1;
125 }
126 }
127 int main(){
128 int p = 0,
129 row = 1;
130 printf("输入测试语句：");
131 do{
132 ch = getchar();
133 savearray[p++] = ch;
134 }while(ch != '#');
135
136 p = 0;
137 do{
138 getarrays();
139 switch(arrays){
140 case -1:
141 printf("第%d行有问题",row);
142 break;
143 case 100:
144 row += 1;
145 break;
146 case 11:
147 printf("(%d,%d)\n", count,arrays);
148 break;
149 default:
150 printf("(%s,%d)\n",outarray,arrays);
151 }
152 }while(arrays != 0);
153 }
154
155
156
