一、实验题目

根据给定文法编写调试预测分析程序，对任意输入串用预测分析法进行语法分析。

二、实验目的

加深对预测分析法的理解。

三、实验内容

四、实验代码

#include <iostream> 
#include <stdio.h> 
#include <string> 
#include <stack> 
using namespace std; 
char Vn[] = { 'E','e','T','t','F' }; //定义文法的非终结符，小写字母e表示E’
char Vt[] = { 'i','+','*','(',')','#' };//定义文法的终结符 
int LENVt = sizeof(Vt); 
void showstack(stack<char> st) //从栈底开始显示栈中的内容 
{ 
int i, j; 
char ch[100]; 
j = st.size(); 
for (i = 0; i < j; i++) 
{ 
ch[i] = st.top(); //依次获取栈顶元素并赋值给ch数组 
st.pop(); //栈顶元素出栈 
} 
for (i = j - 1; i >= 0; i--) 
{ 
cout << ch[i]; //逆序打印ch数组里的的元素 
st.push(ch[i]);//元素逆序入栈 
} 
} 
int find(char c, char array[], int n)//在array数组中查找字符c 
{ 
int i; 
int flag = 0; 
for (i = 0; i < n; i++) 
{ 
if (c == array[i]) 
flag = 1; 
} 
return flag; 
} 
int location(char c, char array[])//在array数组中查找字符c,若查找成功返回字 
//符c的下标 
{ 
int i; 
for (i = 0; c != array[i]; i++); 
return i; 
} 
void error()//打印程序出错信息 
{ 
cout << " error!" << endl; 
}
void analyse(char Vn[], char Vt[], string M[5][6], string str) 
{ 
int i, j, p, q, h, flag = 1; 
char a, X; 
stack<char> st; 
st.push('#');//‘#’入栈。 
st.push(Vn[0]);//Vn[0]入栈 
j = 0; 
//j指向输入串的指针 
h = 1; 
a = str[j]; 
cout << "步骤 " << "分析栈 " << "剩余输入串 " << "所用产生式" << endl; 
while (flag == 1) 
{ 
cout << h << " ";//显示步骤 
h++; 
showstack(st); //显示分析栈中内容 
cout << " "; 
for (i = j; i < str.size(); i++) 
cout << str[i]; //显示剩余字符串 
X = st.top(); 
if (find(X, Vt, LENVt) == 1) 
if (X == a) //分析栈的栈顶元素和剩余输入串的第一个元素相较 
if (X != '#') 
{ 
cout << " " << X << "匹配" << endl; 
st.pop(); 
a = str[++j]; 
//读入输入串的下一个字符 
} 
else 
{ 
cout << " " << "接受！" << endl << endl; 
flag = 0; 
} 
else 
{ 
error(); 
break; 
} 
else{ 
for (p = 0; p < sizeof(Vn); p++){
if(X == Vn[p]){
break;
}
}
//实现下标的转化（非终结符转换为行下标） 
for(q = 0; q < LENVt; q++){
if(a == Vt[q]){
break;
}
}
//实现下标的转化（终结符转换为列下标） 
string S1("NULL"), S2("null"); 
if (M[p][q] == S1 || M[p][q] == S2) 
//查找二维数组中的产生式 
{ 
error(); 
break; //对应项为空，则出错 
} 
else 
{ 
string str0 = M[p][q]; 
cout << " " << X << "-->" << str0 << endl; //显示相应生式 
st.pop(); 
if (str0 != "$") //$代表“空”字符 
for (i = str0.size() - 1; i >= 0; i--){ 
st.push(str0[i]);
}
//产生式右端逆序进栈 
} 
} 
} 
} 
int main() 
{ 
string M[5][6] = { "Te","NULL","NULL","Te","NULL","NULL", 
"NULL","+Te","NULL","NULL","$","$", 
"Ft","NULL","NULL","Ft","NULL","NULL", 
"NULL","$","*Ft","NULL","$","$", 
"i","NULL","NULL","(E)","NULL","NULL" 
};//预测分析表 
string str; 
int errflag, i; 
cout << "文法：E->E+T|T T->T*F|F F->(E)|i" << endl; 
cout << "请输入分析串（以#结束）：" << endl; 
do 
{ 
errflag = 0; 
cin >> str; 
for (i = 0; i < str.size(); i++)if (!find(str[i], Vt, LENVt)) 
{ 
cout << "输入串中包含非终结符" << str[i] << "（输入错误）！" << endl; 
errflag = 1; 
} 
} while (errflag == 1); 
analyse(Vn, Vt, M, str); 
return 0; 
}

五、实验结果

正确识别：

错误识别：