编译技术实验2：递归下降语法分析
作者：互联网
源代码
#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
using namespace std;
const char* keyword[8] = { "if","for","else","while","do","float","int",
"break" };
char keywordtable[20][20], re_keywordtable[20][20];
char digittable[20][20], re_digittable[20][20];
char otherchartable[20][20], re_otherchartable[20][20];
char idtable[20][20], re_idtable[20][20];
char notetable[20][20];
char finaltable[100][20];
int finaltableint[100];
char word[20];
void initialize();
void alpha();
void digit();
void error();
void otherchar();
void note();
void print();
void program();
void block();
void stmt();
void stmts();
void _bool();
void bool1();
void expr();
void expr1();
void term();
void term1();
void factor();
void match(const char* t);
int digit_num = 0, keyword_num = 0, otherchar_num = 0, id_num = 0, note_num = 0;
int redigit_num = 1, rekeyword_num = 1, reotherchar_num = 1, reid_num = 1;
int final_num = 0, finalnum = 0;
int flag_error = 0, flagerror = 0;
char lookahead;
void main()
{
cout << "请输入要分析的语句:" << endl;
initialize();
while (1)
{
lookahead = cin.get();
if (isalpha(lookahead))
{
alpha();
initialize();
}
else if (isdigit(lookahead))
{
digit();
initialize();
}
else if (lookahead == '\t' || lookahead == ' ')
{
continue;
}
else if (lookahead == '\n')
break;
else if (lookahead == '/')
{
lookahead = cin.get();
if (lookahead == '/' || lookahead == '*')
{
note();
initialize();
}
else
{
cin.putback(lookahead);
strcpy(finaltable[final_num], "/");
strcpy(otherchartable[otherchar_num++], "/");
finaltableint[final_num++] = 2;
initialize();
}
}
else
{
otherchar();
initialize();
}
}
if (flag_error == 0)
{
print();
program();
if (finalnum == final_num&&flagerror==0)
cout << "语法分析完成!" << endl;
}
}
void initialize()
{
for (int i = 0; i < 20; i++)
{
word[i] = '\0';
}
}
void alpha()
{
int i = 1, flag;
char ch = lookahead;
word[0] = ch;
ch = cin.get();
while (isalpha(ch) || isdigit(ch) || ch == '_')
{
word[i++] = ch;
ch = cin.get();
}
cin.putback(ch);
flag = 0;
for (i = 0; i < 8; i++)
{
if (strcmp(word, keyword[i]) == 0)
flag = 1;
}
if (flag == 1)
{
strcpy(keywordtable[keyword_num++], word);
strcpy(finaltable[final_num], word);
for (int k = 1; k <= 8; k++)
{
if (strcmp(word, keyword[k]) == 0)
{
finaltableint[final_num++] = k * 100;
}
}
}
else
{
strcpy(idtable[id_num++], word);
strcpy(finaltable[final_num], "id");
finaltableint[final_num++] = 1;
}
}
void digit()
{
int i = 1;
int flag;
char ch = lookahead;
word[0] = ch;
ch = cin.get();
while (isalpha(ch) || isdigit(ch))
{
word[i++] = ch;
ch = cin.get();
}
cin.putback(ch);
flag = 0;
for (i = 0; word[i] != '\0'; i++)
{
if (word[i] < '0' || word[i]>'9')
flag = 1;
}
if (flag == 1)
{
strcpy(idtable[id_num++], word);
strcpy(finaltable[final_num], "id");
finaltableint[final_num++] = 1;
}
else
{
strcpy(digittable[digit_num++], word);
strcpy(finaltable[final_num], "num");
finaltableint[final_num++] = 99;
}
}
void note()
{
char ch;
int i = 0;
ch = cin.get();
while (1)
{
if (ch == '*')
{
ch = cin.get();
if (ch == '/')
break;
else
{
word[i++] = '*';
word[i++] = ch;
}
}
else
{
word[i++] = ch;
}
ch = cin.get();
}
strcpy(notetable[note_num++], word);
}
void otherchar()
{
char ch;
ch = lookahead;
switch (ch)
{
case'!':
{
ch = cin.get();
if (ch == '=')
{
strcpy(otherchartable[otherchar_num++], "!=");
strcpy(finaltable[final_num], "!=");
finaltableint[final_num++] = 3;
}
else
{
cin.putback(ch);
error();
}
}
break;
case'=':
{
ch = cin.get();
if (ch == '=')
{
strcpy(otherchartable[otherchar_num++], "==");
strcpy(finaltable[final_num], "==");
finaltableint[final_num++] = 4;
}
else
{
strcpy(otherchartable[otherchar_num++], "=");
strcpy(finaltable[final_num], "=");
finaltableint[final_num++] = 5;
cin.putback(ch);
}
}
break;
case'(':
{
strcpy(otherchartable[otherchar_num++], "(");
strcpy(finaltable[final_num], "(");
finaltableint[final_num++] = 6;
}
break;
case')':
{
strcpy(otherchartable[otherchar_num++], ")");
strcpy(finaltable[final_num], ")");
finaltableint[final_num++] = 7;
}
break;
case';':
{
strcpy(otherchartable[otherchar_num++], ";");
strcpy(finaltable[final_num], ";");
finaltableint[final_num++] = 8;
}
break;
case'{':
{
strcpy(otherchartable[otherchar_num++], "{");
strcpy(finaltable[final_num], "{");
finaltableint[final_num++] = 9;
}
break;
case'}':
{
strcpy(otherchartable[otherchar_num++], "}");
strcpy(finaltable[final_num], "}");
finaltableint[final_num++] = 10;
}
break;
case'+':
{
strcpy(otherchartable[otherchar_num++], "+");
strcpy(finaltable[final_num], "+");
finaltableint[final_num++] = 13;
}
break;
case'-':
{
strcpy(otherchartable[otherchar_num++], "-");
strcpy(finaltable[final_num], "-");
finaltableint[final_num++] = 19;
}
break;
case'>':
{
ch = cin.get();
if (ch == '=')
{
strcpy(otherchartable[otherchar_num++], ">=");
strcpy(finaltable[final_num], ">=");
finaltableint[final_num++] = 14;
}
else
{
strcpy(otherchartable[otherchar_num++], ">");
strcpy(finaltable[final_num], ">");
finaltableint[final_num++] = 15;
cin.putback(ch);
}
}
break;
case'<':
{
ch = cin.get();
if (ch == '=')
{
strcpy(otherchartable[otherchar_num++], "<=");
strcpy(finaltable[final_num], "<=");
finaltableint[final_num++] = 16;
}
else
{
strcpy(otherchartable[otherchar_num++], "<");
strcpy(finaltable[final_num], "<");
finaltableint[final_num++] = 17;
}
}
break;
case'*':
{
strcpy(otherchartable[otherchar_num++], "*");
strcpy(finaltable[final_num], "*");
finaltableint[final_num++] = 18;
}
break;
default:
error();
break;
}
}
void error()
{
flag_error = 1;
cout << "出现错误，终止分析！" << endl;
}
void print()
{
finaltableint[final_num] = '\0';
cout << "词法分析结果如下：" << endl;
for (int i = 0; i < final_num; i++)
cout << finaltable[i];
cout << endl;
cout << "语法分析过程如下：" << endl;
}
void program()
{
cout << "program-->block" << endl;
block();
if (flagerror == 1)
{
error();
return;
}
}
void block()
{
if (flagerror == 1)return;
cout << "block-->{stmts}" << endl;
match("{");
stmts();
match("}");
}
void stmts()
{
if (flagerror == 1)return;
if (finaltableint[finalnum] == 10)
{
cout << "stmts-->NULL" << endl;
return;
}
cout << "stmts-->stmt stmts" << endl;
stmt();
stmts();
}
void stmt()
{
if (flagerror == 1)return;
switch (finaltableint[finalnum])
{
case 1:
cout << "stmt-->id=expr;" << endl;
match("id");
match("=");
expr();
match(";");
break;
case 100:
match("if");
match("(");
_bool();
match(")");
stmt();
if (strcmp(finaltable[finalnum], "else") == 0)
{
cout << "stmt-->if(_bool)stmt else stmt" << endl;
match("else");
stmt();
break;
}
else
{
cout << "stmt-->{if(_bool)stmts" << endl;
break;
}
case 400:
cout << "stmt-->while(bool)stmts" << endl;
match("while");
match("(");
_bool();
match(")");
stmt();
break;
case 500:
cout << "stmt-->do stmt while(bool)" << endl;
match("do");
stmt();
match("while");
match("(");
_bool();
match(")");
break;
case 800:
cout << "stmt-->break" << endl;
match("break");
break;
default:
cout << "stmt-->block" << endl;
block();
break;
}
}
void _bool()
{
if (flagerror == 1)
return;
expr();
switch (finaltableint[finalnum])
{
case 17:
cout << "_bool-->expr<expr" << endl;
match("<");
expr();
break;
case 16:
cout << "_bool-->expr<=expr" << endl;
match("<=");
expr();
break;
case 15:
cout << "_bool-->expr>expr" << endl;
match(">");
expr();
break;
case 14:
cout << "_bool-->expr>=expr" << endl;
match(">=");
expr();
break;
default:
cout << "_bool-->expr" << endl;
expr();
break;
}
}
void expr()
{
if (flagerror == 1)return;
cout << "expr-->term expr1" << endl;
term();
expr1();
}
void expr1()
{
if (flagerror == 1)return;
switch (finaltableint[finalnum])
{
case 13:
cout << "expr1-->+ term expr1" << endl;
match("+");
term();
expr1();
break;
case 19:
cout << "expr1-->- term expr1" << endl;
match("-");
term();
expr1();
break;
default:
cout << "expr1-->NULL" << endl;
return;
}
}
void term()
{
if (flagerror == 1)return;
cout << "term-->factor term1" << endl;
factor();
term1();
}
void term1()
{
if (flagerror == 1)return;
switch (finaltableint[finalnum])
{
case 18:
cout << "term1-->* factor term1" << endl;
match("*");
factor();
term1();
break;
case 2:
cout << "term1-->/factor term1" << endl;
match("/");
factor();
term1();
break;
default:
cout << "term1-->NULL" << endl;
return;
}
}
void factor()
{
if (flagerror == 1)
return;
switch (finaltableint[finalnum])
{
case 6:
cout << "factor-->(expr)" << endl;
match("(");
expr();
match(")");
break;
case 1:
cout << "factor-->id" << endl;
match("id");
break;
case 99:
cout << "factor-->num" << endl;
match("num");
break;
default:
flagerror == 1;
break;
}
}
void match(const char* t)
{
if (strcmp(finaltable[finalnum], t) != 0)
{
flagerror = 1;
return;
}
finalnum++;
}标签：语法分析,递归,++,void,编译,num,strcpy,20,final 来源： https://blog.csdn.net/hxy200201/article/details/121322710