词法分析程序的功能:通过用户输入的关键字及其他保留字符,输出它本身及它的种别码
符号与种别码对照表如下
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 |
用文法描述词法规则:
<字母>->a/b/c.../z
<数字>->1/2/3/4/5/6/7/8/9
<标识符>->sum.....
<关键字>->begin/if/then/while/do/end
<运算符>->+,-,*,/,:,:=,<,<=,<>,>,>=,=
<界符>->;|(|)|[|]|{|}
已完成的代码如下:
#include<stdio.h> #include<stdlib.h> #include<string.h> char word[6][5]={"begin","if","then","while","do","end"}; char word2[18][3]={"|","dd*","+","-","*","/",":",":=","<","<=","<>",">",">=","=",";","(",")","#"}; int words(char ch[][5]); int signs(char ch[][3]); main() { char ch[10]; printf("请输入保留字:"); scanf("%s",ch); words(ch); signs(ch); } int words(char ch[][5]) { while(ch==''||ch==10||ch==13||ch==9) { getchar; } if(ch>='a'&&ch<='z') { switch(ch)
{}
} } int signs(char ch[][3]) { while(ch==''||ch==10||ch==13||ch==9) { getchar; } if(ch>='0'&&ch<='9') { switch(ch)
{} } }