【实验目的】
掌握算符优先分析法的原理，利用算符优先分析法将赋值语句进行语法分析。
【实验内容】
（1）输入一个文法根据算符优先分析法，将表达式进行语法分析，判断一个表达式是否为算符优先文法
(2)输入一个句子进行分析
【实验要求】
1、根据文法求FIRSTVT集和LASTVT集
给定一个上下文无关文法，根据算法设计一个程序，求文法中每个非终结符的FirstVT 集和LastVT 集。
可参考算法描述如下：
/*求 FirstVT 集的算法*/
PROCEDURE insert(P,a);
IF not F[P,a] then
begin
F[P,a] = true; //(P,a)进栈
end;
Procedure FirstVT;
Begin
for 对每个非终结符 P和终结符 a do
F[P,a] = false
for 对每个形如 P a…或 P→Qa…的产生式 do
Insert(P,a)
while stack 非空
begin
栈顶项出栈，记为(Q,a)
for 对每条形如 P→Q…的产生式 do
insert(P,a)
end;
end.
同理，可构造计算LASTVT的算法。
2、构造算符优先分析表
依据文法和求出的相应FirstVT和 LastVT 集生成算符优先分析表。
参考算法描述如下：
for 每个形如 P->X1X2…Xn的产生式 do
for i =1 to n-1 do
begin
if Xi和Xi+1都是终结符 then
Xi = Xi+1
if i<= n-2, Xi和Xi+2 是终结符, 但Xi+1 为非终结符 then
Xi = Xi+2
if Xi为终结符, Xi+1为非终结符 then
for FirstVT 中的每个元素 a do
Xi < a ;
if Xi为非终结符, Xi+1为终结符 then
for LastVT 中的每个元素 a do
a > Xi+1 ;
end
3、构造控制程序
参考 算法描述如下：
stack S;
k = 1; //符号栈S的使用深度
S[k] = ‘#’
REPEAT
把下一个输入符号读进a中；
If S[k] VT then j = k else j = k-1;
While S[j] > a do
Begin
Repeat
Q = S[j];
if S[j-1] VT then j = j-1 else j = j-2
until S[j] < Q;
把S[j+1]…S[k]归约为某个N，并输出归约为哪个符号；
K = j+1;
S[k] = N;
end of while
if S[j] < a or S[j] = a then
begin k = k+1; S[k] = a end
else error //调用出错诊察程序
until a = ‘#’
4、对给定的表达式，给出准确与否的分析过程
5、给出表达式的计算结果。
【实验结果】
图为参考，要求包含firstvt和lastvt集，算符优先表或优先函数表及句子分析过程。
实验截图：
代码：
1 Mian.cpp:
2 #include <stdio.h>
3 #include <math.h>
4 #include <string.h>
5 #include <stdlib.h>
6 #include <iostream>
7 #include <sstream>
8 #include <algorithm>
9 #include <set>
10 #include <queue>
11 #include <stack>
12 #include <map>
13 #include <bitset>
14 #pragma comment(linker, "/STACK:102400000,102400000")
15 typedef long long LL;
16 const int inf = 0x3f3f3f3f;
17 const double pi = acos(-1.0);
18 const double esp = 1e-6;
19 using namespace std;
20
21 const int Maxn = 110;
22 const int maxn = 20;
23 char str[maxn][Maxn];//输入文法
24 char st[maxn];//输入串
25 char stac[maxn];//模拟栈的数组
26 char nstr[maxn][maxn];//储存转化文法
27 char mstr[maxn][maxn];
28 char fin[maxn];//存储终结符
29 char firstvt[maxn][maxn], lastvt[maxn][maxn];
30 char cmp[maxn][maxn];//存储表中的比较符
31 int firstflag[maxn], lastflag[maxn];//非终结符的firstvt,lastvt是否求出
32 int fcnt[maxn], lcnt[maxn];//非终结符firsvt和lastvt的个数
33 int is_fin(char c) { //判断终结符
34 for (int i = 0; fin[i] != ‘\0‘; i++) {
35 if (fin[i] == c)
36 return 1;
37 }
38 return 0;
39 }
40 int site(char c) { //求在表中的下标
41 for (int i = 0; fin[i] != ‘\0‘; i++) {
42 if (fin[i] == c)
43 return i;
44 }
45 }
46
47 void get_firstvt(char s, int t) { //求s非终结符的firstvt值
48 int i, j, ii, jj, tt;
49 for (i = 0; i<t; i++) {
50 if (str[i][0] == s)
51 break;
52 }
53 if (!firstflag[i]) {
54 int k = fcnt[i];
55 for (j = 0; str[i][j] != ‘\0‘; j++) {
56 if (j == 2 || str[i][j] == ‘|‘) {
57 if (is_fin(str[i][j + 1])) {
58 firstvt[i][k++] = str[i][j + 1];
59 }
60 else {
61 if (is_fin(str[i][j + 2])) {
62 firstvt[i][k++] = str[i][j + 2];
63 }
64 if (str[i][j + 1] != s) {
65 get_firstvt(str[i][j + 1], t);
66 for (ii = 0; ii<t; ii++) {
67 if (str[ii][0] == str[i][j + 1])
68 break;
69 }
70 for (jj = 0; jj<fcnt[ii]; jj++) {
71 for (tt = 0; tt<k; tt++) {
72 if (firstvt[i][tt] == firstvt[ii][jj])
73 break;
74 }
75 if (tt == k) {
76 firstvt[i][k++] = firstvt[ii][jj];
77 }
78 }
79 }
80 }
81 }
82 }
83 firstvt[i][k] = ‘\0‘;
84 fcnt[i] = k;
85 firstflag[i] = 1;
86 }
87 }
88
89 void output_firstvt(int T) { //输出firstvt集
90 for (int i = 0; i<T; i++) {
91 get_firstvt(str[i][0], T);
92 }
93 for (int i = 0; i<T; i++) {
94 printf("Firstvt[%c]:", str[i][0]);
95 for (int j = 0; j<fcnt[i]; j++) {
96 printf("%c ", firstvt[i][j]);
97 }
98 puts("");
99 }
100 }
101
102 void get_lastvt(char s, int t) { //求s非终结符的lastvt值
103 int i, j, ii, jj, tt;
104 for (i = 0; i<t; i++) {
105 if (str[i][0] == s)
106 break;
107 }
108 if (!lastflag[i]) {
109 int k = lcnt[i];
110 for (j = 0; str[i][j] != ‘\0‘; j++) {
111 if (str[i][j + 1] == ‘|‘ || str[i][j + 1] == ‘\0‘) {
112 if (is_fin(str[i][j])) {
113 lastvt[i][k++] = str[i][j];
114 }
115 else {
116 if (is_fin(str[i][j - 1])) {
117 lastvt[i][k++] = str[i][j - 1];
118 }
119 if (str[i][j] != s) {
120 get_lastvt(str[i][j], t);
121 for (ii = 0; ii<t; ii++) {
122 if (str[ii][0] == str[i][j])
123 break;
124 }
125 for (jj = 0; jj<lcnt[ii]; jj++) {
126 for (tt = 0; tt<k; tt++) {
127 if (lastvt[i][tt] == lastvt[ii][jj])
128 break;
129 }
130 if (tt == k) {
131 lastvt[i][k++] = lastvt[ii][jj];
132 }
133 }
134 }
135 }
136 }
137 }
138 lastvt[i][k] = ‘\0‘;
139 lcnt[i] = k;
140 lastflag[i] = 1;
141 }
142 }
143
144 void output_lastvt(int T) { //输出lastvt集
145 for (int i = 0; i<T; i++) {
146 get_lastvt(str[i][0], T);
147 }
148 for (int i = 0; i<T; i++) {
149 printf("Lastvt[%c]:", str[i][0]);
150 for (int j = 0; j<lcnt[i]; j++) {
151 printf("%c ", lastvt[i][j]);
152 }
153 puts("");
154 }
155 }
156
157 void get_table(int T, int cnt) { //得到表
158 int x = 0, y = 0;
159 int i, j, ii, jj;
160 for (i = 0; i<T; i++) {
161 for (j = 0; str[i][j] != ‘\0‘; j++) {
162 if (str[i][j] != ‘|‘)
163 nstr[x][y++] = str[i][j];
164 else if (str[i][j] == ‘|‘) {
165 nstr[x][y] = ‘\0‘;
166 x++;
167 y = 0;
168 nstr[x][y++] = str[i][0];
169 nstr[x][y++] = ‘-‘;
170 nstr[x][y++] = ‘>‘;
171 }
172 }
173 nstr[x][y] = ‘\0‘;
174 x++;
175 y = 0;
176 }
177 //对于S1->#S#;
178 char a = ‘#‘;
179 cmp[site(a)][site(a)] = ‘=‘;
180 for (i = 0; i<fcnt[0]; i++) {
181 cmp[site(a)][site(firstvt[0][i])] = ‘<‘;
182 }
183 for (i = 0; i<lcnt[0]; i++) {
184 cmp[site(lastvt[0][i])][site(a)] = ‘>‘;
185 }
186 //对于初始的文法
187 for (i = 0; i<x; i++) {
188 for (j = 3; nstr[i][j + 1] != ‘\0‘; j++) {
189 if (is_fin(nstr[i][j]) && is_fin(nstr[i][j + 1]))
190 cmp[site(nstr[i][j])][site(nstr[i][j + 1])] = ‘=‘;
191 if (is_fin(nstr[i][j]) && !is_fin(nstr[i][j + 1]) && is_fin(nstr[i][j + 2]) && nstr[i][j + 2] != ‘\0‘)
192 cmp[site(nstr[i][j])][site(nstr[i][j + 2])] = ‘=‘;
193 if (!is_fin(nstr[i][j]) && is_fin(nstr[i][j + 1])) { //对于非终结符在终结符之前
194 for (ii = 0; ii<T; ii++) {
195 if (str[ii][0] == nstr[i][j])
196 break;
197 }
198 for (jj = 0; jj<lcnt[ii]; jj++)
199 cmp[site(lastvt[ii][jj])][site(nstr[i][j + 1])] = ‘>‘;
200 }
201 if (is_fin(nstr[i][j]) && !is_fin(nstr[i][j + 1])) { //对于终结符在非终结符之前
202 for (ii = 0; ii<T; ii++) {
203 if (str[ii][0] == nstr[i][j + 1])
204 break;
205 }
206 for (jj = 0; jj<fcnt[ii]; jj++)
207 cmp[site(nstr[i][j])][site(firstvt[ii][jj])] = ‘<‘;
208 }
209 }
210 }
211 for (i = 0; fin[i] != ‘\0‘; i++)
212 printf("\t%c", fin[i]);
213 puts("");
214 for (i = 0; i<cnt; i++) {
215 printf("%c\t", fin[i]);
216 for (j = 0; j<cnt; j++) {
217 if (cmp[i][j] != 0)
218 printf("%c\t", cmp[i][j]);
219 else
220 printf(" \t");
221 }
222 puts("");
223 }
224
225 }
226 void output(int i, int j, char *str) {
227 printf("\t");
228 for (int ii = i; ii <= j; ii++)
229 printf("%c", str[ii]);
230 }
231
232 int isDX(char c)
233 {
234 if (c >= ‘A‘&&c <= ‘Z‘)
235 return 1;
236 return 0;
237 }
238 void exchange()
239 {
240 int ecnt = 0;
241 for (int i = 0; i<10; i++) {
242 int mcnt = 0;
243 for (int j = 3; nstr[i][j] != ‘\0‘; j++) {
244 if (isDX(nstr[i][j]) && strlen(nstr[i]) != 4)
245 mstr[ecnt][mcnt++] = ‘N‘;
246 else if (!isDX(nstr[i][j]))
247 mstr[ecnt][mcnt++] = nstr[i][j];
248 else {
249 break;
250 }
251 }
252 mstr[ecnt][mcnt] = ‘\0‘;
253 if (strlen(mstr[ecnt]) != 0)
254 ecnt++;
255 }
256 }
257 int get_process(char *st)//
258 {
259 exchange();
260 int len = strlen(st);
261 int t = 0;//栈内元素的个数
262 int i = 0, j;
263 int bz = 1;
264 stac[0] = ‘#‘;
265 while (st[i] != ‘\0‘) {
266 if (is_fin(stac[t])) j = t;
267 else j = t - 1;
268 int a = site(stac[j]);
269 int b = site(st[i]);
270 if (cmp[a][b] == ‘<‘ || cmp[a][b] == ‘=‘) {
271 printf("\t%d", bz++);
272 output(0, t, stac);
273 printf("\t%c", cmp[a][b]);
274 printf("\t%c", st[i]);
275 output(i + 1, len - 1, st);
276 printf("\t移进");
277 puts("");
278 t++;
279 stac[t] = st[i];
280 i++;
281 }
282 else if (cmp[a][b] == ‘>‘) {
283 printf("\t%d", bz++);
284 output(0, t, stac);
285 printf("\t%c", cmp[a][b]);
286 printf("\t%c", st[i]);
287 output(i + 1, len - 1, st);
288 printf("\t归约");
289 puts("");
290 int ii, jj, kk;
291 int flag = 0;
292 for (ii = t; ii >= 0; ii--) {
293 for (jj = 0; jj<maxn; jj++) {
294 int lee = strlen(mstr[jj]);
295 int kkn = 0;
296 for (kk = lee - 1; kk >= 0; kk--) {
297 if (stac[ii] == mstr[jj][kk]) {
298 ii--;
299 kkn++;
300 }
301 else
302 break;
303 }
304 if (strlen(mstr[jj]) == kkn) {
305 t = ii + 1;
306 stac[t++] = ‘N‘;
307 stac[t] = ‘\0‘;
308 t--;
309 flag = 1;
310 break;
311 }
312 else {
313 ii = ii + kkn;
314 }
315 }
316 if (!flag) {
317 printf("\t错误");
318 return 0;
319 }
320 else {
321 if (t == 1 && st[i] == ‘#‘) {
322 printf("\t%d", bz++);
323 output(0, t, stac);
324 printf("\t=");
325 printf("\t%c", st[i]);
326 output(i + 1, len, st);
327 printf("\t接受");
328 return 1;
329 }
330 break;
331 }
332 }
333 }
334 }
335 }
336 int main() {
337 int T;
338 int cnt = 0;//终结符的个数
339 for (int i = 0; i < 10; i++)
340 cout << "*********";
341 cout << endl;
342 cout << "周博（20173599）" << endl;
343 for (int i = 0; i < 10; i++)
344 cout << "*********";
345 cout << endl;
346 memset(firstflag, 0, sizeof(firstflag));
347 memset(lastflag, 0, sizeof(lastflag));
348 memset(cmp, 0, sizeof(cmp));
349 cout << "请输入文法规则数：";
350 cin >> T;
351 cout << "请输入文法规则：" << endl;
352 for (int i = 0; i < T; i++) {
353 cin >> str[i];
354 fcnt[i] = lcnt[i] = 0;
355 }
356 //让输入的格式化
357 int oo = 0;
358 int mm = T;
359 //int column = sizeof(str[0]) / sizeof(char);
360 char str_str[maxn][Maxn];//输入文法
361 for (int i = 0; i < maxn; i++) {
362 for (int j = 0; j<Maxn; j++)
363 {
364 str_str[i][j] = ‘\0‘;
365 }
366 }
367 for (int i = 0; i < mm; i++) {
368 for (int j = 0; str[i][j] != ‘\0‘; j++)
369 {
370 str_str[i][j] = str[i][j];
371 }
372 }
373 int TT = T;
374 for (int i = 0; i<mm; i++) {
375 for (int j = 0; str_str[i][j] != ‘\0‘; j++)
376 {
377 int column = 0;
378 for (column = 0; str_str[i][column] != ‘\0‘; column++)
379 {
380
381 }
382 column += 1;
383 if (str_str[i][j] == ‘>‘)
384 {
385 oo = j;
386
387 }
388 if (str_str[i][j] == ‘|‘)
389 {
390 char str_f[Maxn];
391 for (int qq = 0; qq < column; qq++)
392 {
393 str_f[qq] = str_str[i][qq];
394 }
395 for (int qq = j; qq < column; qq++)
396 {
397 str_str[i][qq] = ‘\0‘;
398 }
399
400
401
402 TT = TT + 1;
403 for (int qq = 0; qq < oo + 1; qq++)
404 {
405 str_str[TT-1][qq] = str_f[qq];
406 }
407 int mid = oo + 1;
408 for (int qq = j + 1; qq < column; qq++)
409 {
410 str_str[TT - 1][mid] = str_f[qq];
411 mid = mid + 1;
412 }
413 for (int qq = 0; qq < column; qq++)
414 {
415 cout << str_str[TT - 1][qq];
416 }
417 break;
418 }
419 }
420
421 }
422 cout << endl;
423 for (int i = 0; i < TT; i++)
424 {
425 cout << i + 1 << ": " << str_str[i] << endl;
426 }
427 for (int i = 0; i<T; i++) {
428 for (int j = 0; str[i][j] != ‘\0‘; j++) {
429 if ((str[i][j]<‘A‘ || str[i][j]>‘Z‘) && (str[i][j] != ‘-‘&&str[i][j] != ‘>‘) && str[i][j] != ‘|‘)
430 fin[cnt++] = str[i][j];
431 }
432 }
433 fin[cnt++] = ‘#‘;
434 fin[cnt] = ‘\0‘;
435 cout << "FIRSTUT集为：" << endl;
436 output_firstvt(T);
437 cout << endl;
438 cout << "LASTUT集为：" << endl;
439 output_lastvt(T);
440 cout << "算符优先分析表如下：" << endl;
441 get_table(T, cnt);
442 cout << "请输入文法输入符号以#结束：";
443 //scanf("%s", st);
444 cin >> st;
445 get_process(st);
446 int a;
447 cin >> a;
448 return 0;
449 }
原文地址：https://www.cnblogs.com/smartisn/p/12207412.html
时间： 2024-11-08 05:34:09