语法分析器在词法分析器的基础上增加了递归下降分析程序，咱也不知道啥是递归下降程序，咱也不想问。 但是有程序框图和伪代码把程序跑通咱还是比较在行滴。为了便于理解，debug过程中的输出也保留了。
下面是完整代码。
1 /* 2 begin a:= 9; x:=2*3;b:=a+x end# 3 x:= a+b*c end # 4 */ 5 #include6 #include 7 #include 8 #define _KEY_WORD_END "waiting for your expanding" 9 typedef struct 10 { 11 int typenum; 12 char *word; 13 }WORD; 14 char input[255]; 15 char token[255]=""; 16 int p_input; 17 int p_token; 18 char ch; 19 char* rwtab[] = { "begin","if","then","while","do","end",_KEY_WORD_END}; 20 WORD * scaner(); 21 WORD* oneword = new WORD; 22 int syn,kk; 23 void expression(); 24 void factor() 25 { 26 if(syn == 10 || syn == 11) 27 { 28 oneword = scaner(); 29 syn = oneword->typenum; 30 printf("%s %d\n",oneword->word,syn); 31 } 32 else if(syn == 27) 33 { 34 oneword = scaner(); 35 syn = oneword->typenum; 36 printf("%s %d\n",oneword->word,syn); 37 expression(); 38 if(syn == 28) 39 { 40 oneword = scaner(); 41 syn = oneword->typenum; 42 printf("%s %d\n",oneword->word,syn); 43 } 44 else{ 45 printf("右括号错误\n"); 46 kk = 1; 47 } 48 } 49 else 50 { 51 printf("表达式错误\n"); 52 kk = 1; 53 } 54 return; 55 } 56 void term() 57 { 58 factor(); 59 while(syn == 15 || syn == 16) 60 { 61 oneword = scaner(); 62 syn = oneword->typenum; 63 printf("%s %d\n",oneword->word,syn); 64 factor(); 65 } 66 return; 67 } 68 void expression() 69 { 70 term(); 71 while(syn == 13 || syn == 14) 72 { 73 oneword = scaner(); 74 syn = oneword->typenum; 75 printf("%s %d\n",oneword->word,syn); 76 term(); 77 } 78 return; 79 } 80 void statement() 81 { 82 if(syn == 10) 83 { 84 oneword = scaner(); 85 syn = oneword->typenum; 86 printf("%s %d\n",oneword->word,syn); 87 if(syn == 18) 88 { 89 oneword = scaner(); 90 syn = oneword->typenum; 91 printf("%s %d\n",oneword->word,syn); 92 expression(); 93 } 94 else{ 95 printf("赋值号错误\n"); 96 kk = 1; 97 } 98 } 99 else{100 printf("语句错误\n");101 kk = 1;102 }103 return;104 }105 void yucu()106 {107 statement();108 while(syn == 26)109 {110 oneword = scaner();111 syn = oneword->typenum;112 printf("%s %d\n",oneword->word,syn);113 statement();114 }115 return;116 }117 void Irparser()118 {119 if(syn == 1)120 {121 oneword = scaner();122 syn = oneword->typenum;123 printf("%s %d\n",oneword->word,syn);124 yucu();125 126 if(syn==6)127 {128 oneword = scaner();129 syn = oneword->typenum;130 if(syn == 0 && (kk == 0))131 printf("success\n");132 }133 else{134 if(kk != 1)135 {136 printf("缺少end错误\n");137 kk = 1;138 }139 }140 }141 else{142 printf("begin错误\n");143 kk = 1;144 }145 return;146 }147 int main()148 {149 int over = 1;150 151 printf("Enter Your words(end with #):");152 scanf("%[^#]s",input);153 p_input = 0;154 printf("Your words:\n%s\n",input);155 156 //获取下一个单词符号157 oneword = scaner();158 syn = oneword->typenum;159 Irparser();160 161 printf("\npress # to exit:");162 scanf("%[^#]s",input);163 return 0;164 }165 char m_getch()166 {167 ch = input[p_input];168 p_input = p_input+1;169 return(ch);170 }171 void getbc()172 {173 while(ch == ' '||ch == 10)174 {175 ch = input[p_input];176 p_input++;177 }178 }179 void concat()180 {181 token[p_token] = ch;182 p_token++;183 token[p_token] = '\0';184 }185 int letter()186 {187 if((ch >= 'a'&& ch <= 'z')|| (ch >='A'&&ch <= 'Z'))188 return 1;189 else190 return 0;191 }192 int digit()193 {194 if(ch >= '0'&&ch <='9')return 1;195 else return 0;196 }197 int reserve()198 {199 int i = 0;200 while(strcmp(rwtab[i],_KEY_WORD_END))201 {202 if(!strcmp(rwtab[i],token))203 return i+1;204 i++;205 }206 return 10;207 }208 void retract()209 {210 p_input--;211 }212 213 char* dtb()214 {215 return NULL;216 }217 218 WORD* scaner()219 {220 221 WORD* myword = new WORD;222 myword->typenum = 10;223 myword->word = "";224 p_token = 0;225 m_getch();226 getbc();227 if(letter())228 {229 while(letter()||digit())230 {231 concat();232 m_getch();233 }234 retract();235 myword->typenum = reserve();236 myword->word = token;237 return(myword);238 }239 else if(digit())240 {241 while(digit())242 {243 concat();244 m_getch();245 }246 retract();247 myword->typenum = 11;248 myword->word = token;249 return(myword);250 }251 else switch(ch)252 {253 case'=':m_getch();254 if(ch == '=')255 {256 myword->typenum = 25;257 myword->word = "==";258 return(myword);259 }260 retract();261 myword->typenum = 21;262 myword->word = "=";263 return(myword);264 break;265 case'+':266 myword->typenum = 13;267 myword->word = "+";268 return(myword);269 break;270 case'-':271 myword->typenum = 14;272 myword->word = "-";273 return(myword);274 break;275 case'*':276 myword->typenum = 15;277 myword->word = "*";278 return(myword);279 break;280 case'/':281 myword->typenum = 16;282 myword->word = "/";283 return(myword);284 break;285 case'(':286 myword->typenum = 27;287 myword->word = "(";288 return(myword);289 break;290 case')':291 myword->typenum = 28;292 myword->word = ")";293 return(myword);294 break;295 case'[':296 myword->typenum = 28;297 myword->word = "[";298 return(myword);299 break;300 case']':301 myword->typenum = 29;302 myword->word = "]";303 return(myword);304 break;305 case'{ ':306 myword->typenum = 30;307 myword->word = "{ ";308 return(myword);309 break;310 case'}':311 myword->typenum = 31;312 myword->word = "}";313 return(myword);314 break;315 case',':316 myword->typenum = 32;317 myword->word = ",";318 return(myword);319 break;320 case':':m_getch();321 if(ch == '=')322 {323 myword->typenum = 18;324 myword->word = ":=";325 return(myword);326 }327 retract();328 myword->typenum = 17;329 myword->word = ":";330 return(myword);331 break;332 case';':333 myword->typenum = 26;334 myword->word = ";";335 return(myword);336 break;337 case'>':m_getch();338 if(ch == '=')339 {340 myword->typenum = 24;341 myword->word = ">=";342 return(myword);343 }344 retract();345 myword->typenum = 23;346 myword->word = ">";347 return(myword);348 break;349 case'<':m_getch();350 if(ch == '=')351 {352 myword->typenum = 22;353 myword->word = "<=";354 return(myword);355 }356 else if(ch == '>')357 {358 myword->typenum = 21;359 myword->word = "<>";360 return(myword);361 }362 retract();363 myword->typenum = 20;364 myword->word = "<";365 return(myword);366 break;367 case'!':m_getch();368 if(ch == '=')369 {370 myword->typenum = 40;371 myword->word = "!=";372 return(myword);373 }374 retract();375 myword->typenum = -1;376 myword->word = "ERROR";377 return(myword);378 break;379 case'#':380 myword->typenum = 0;381 myword->word = "#";382 return(myword);383 break;384 case'\0':385 myword->typenum = 0;386 myword->word = "OVER";387 return(myword);388 break;389 default: myword->typenum = -1;390 myword->word = "ERROR";391 return(myword);392 }393 }