标签：判断 exit git bit containe ref iterator ide its
最后一次实验！
【问题描述】
在实验二或实验三的表达式语法分析程序里，添加语义处理部分。 对于语法正确的表达式，输出其中间代码，用四元式序列表示；对于语法正确的算术表达式，输出其计算值。例如：当输入为2+35时，程序输出为17；当输入为a(b+c)时，程序输出为四元式：
(+,b,c,t1)
(,a,t1,t2)
要求源程序能智能判断这两种情况，并输出相应结果。
【输入形式】
（1） PL/0算术表达式的语义计算。PL/0算术表达式，例如:2+35作为输入。
（2）PL/0表达式的中间代码表示。输入：PL/0表达式，例如: a*(b+c)。
【输出形式】
2+35作为输入时，输出为17
a(b+c)作为输入时，输出为
(+,b,c,t1)
(*,a,t1,t2)
#include <iostream>
#include<bits/stdc++.h>
using namespace std;
/**词法分析及其结果存储**/
pair<string, string> lexRes[50]; // 词法分析结果，每个pair的first如"ident"，second如"a"
int lexI = 0; // lexRes的指针
void lexical()
/*词法分析：读入一行字符串，处理该字符串的词法分析结果至lexRes*/
/*lexI终为lexRes的长度，即单词数*/
{
// 读入输入串
string inputs; // 如，a*(b+c)
cin >> inputs;
// 初始化词典
map<string,string> words;
std::map<string,string>::iterator it;
words["+"]="plus";
words["-"]="minus";
words["*"]="times";
words["/"]="slash";
words["="]="eql";
words["("]="lparen";
words[")"]="rparen";
// 开始分析
int insize=inputs.length();
string word; // 输入符号，如"a"/"123"
for(int i=0; i<insize; i++)
{
// 空白符跳过
while(inputs[i] == ‘ ‘ || inputs[i] == ‘\n‘)
i++;
// 标志符/基本字捕捉
if(isalpha(inputs[i])){
// 拿出一个标志符/基本字
word = inputs[i++];
while(isalpha(inputs[i]) || isdigit(inputs[i]))
word += inputs[i++];
// 在map中找到相应的词性，并输出
it = words.find(word);
if(it != words.end())
lexRes[lexI++] = make_pair(words[word], word);
// cout << "(" << words[word] << "," << word << ")" << endl;
else
lexRes[lexI++] = make_pair("ident", word);
// cout << "(ident" << "," << word << ")" << endl;
i--;
}
// 常数
else if(isdigit(inputs[i])){
// 拿出常数
word=inputs[i++];
while(isdigit(inputs[i]))
word+=inputs[i++];
lexRes[lexI++] = make_pair("number", word);
//cout << "(number" << "," << word << ")" << endl;
i--;
}
// <、<=号
else if(inputs[i]==‘<‘){
word=inputs[i++];
if(inputs[i]==‘>‘){
word+=inputs[i];
lexRes[lexI++] = make_pair(words[word], word);
// cout << "(" << words[word] << "," << word << ")" << endl;
}else if(inputs[i]==‘=‘){
word+=inputs[i];
lexRes[lexI++] = make_pair(words[word], word);
// cout << "(" <<words[word] << "," << word << ")" << endl;
}else if(inputs[i]!=‘ ‘||!isdigit(inputs[i])||!isalpha(inputs[i])){
lexRes[lexI++] = make_pair(words[word], word);
// cout << "(" << words[word] << "," << word << ")" << endl;
}else{
//cout << "error!" << endl;
}
i--;
}
// >、>=
else if(inputs[i]==‘>‘){
word=inputs[i++];
if(inputs[i]==‘=‘){
word+=inputs[i];
lexRes[lexI++] = make_pair(words[word], word);
// cout<<"("<<words[word]<<","<<word<<")"<<endl;
}else if(inputs[i]!=‘ ‘||!isdigit(inputs[i])||!isalpha(inputs[i])){
lexRes[lexI++] = make_pair(words[word], word);
// cout<<"("<<words[word]<<","<<word<<")"<<endl;
}else{
//cout<<"error!"<<endl;
}
i--;
}
//:=
else if(inputs[i]==‘:‘){
word=inputs[i++];
if(inputs[i]==‘=‘){
word+=inputs[i];
lexRes[lexI++] = make_pair(words[word], word);
// cout<<"("<<words[word]<<","<<word<<")"<<endl;
}else{
//cout<<"error!"<<endl;
}
//i--;
}
//其他的基本字
else{
word=inputs[i];
it=words.find(word);
if(it!=words.end()){
lexRes[lexI++] = make_pair(words[word], word);
// cout<<"("<<words[word]<<","<<word<<")"<<endl;
}else{
//cout<<"error!"<<endl;
}
}
}
}
/**四元式相关，被调用**/
struct quad{
string result;
string arg1;
string arg2;
string op;
};
struct quad quad[50]; // 四元式数组
int quaI = 0; // 指向四元式的指针
void emit(string op, string arg1, string arg2, string result)
/*发射一行四元式*/
{
quad[quaI].op = op;
quad[quaI].arg1 = arg1;
quad[quaI].arg2 = arg2;
quad[quaI].result = result;
quaI++;
}
int tI = 1; // 记录当前是t1/t2...t几了
string newT()
/*产生一个t1/t2...*/
{
stringstream ss;
ss << tI;
string ti = "t" + ss.str();
tI++;
return ti;
}
/**非算数表达式的递归下降分析及四元式生成**/
// 指针前进
int sym=0; // 正在处理的单词
void advance()
{
++sym;
if(sym > lexI){
cout << "ERROR!sym指针越界";
exit(0);
}
}
string E();
string T();
string F();
string F()
/*因子分析*/
{
string arg;
if(lexRes[sym].first == "ident"){
arg = lexRes[sym].second;
advance();
}
else if(lexRes[sym].first == "number"){
arg = lexRes[sym].second;
advance();
}
else if(lexRes[sym].first == "lparen"){
advance();
arg = E();
if(lexRes[sym].first == "rparen"){
advance();
}
else{
cout << "ERROR!未能匹配右括号！语法错误\n";
exit(0);
}
}
return arg;
}
string T()
/*项分析*/
{
string op, arg1, arg2, result;
arg1 = F();
while(lexRes[sym].first == "times" || lexRes[sym].first == "slash"){
op = lexRes[sym].second;
advance();
arg2 = F();
result = newT();
emit(op, arg1, arg2, result);
arg1 = result;
}
return arg1;
}
string E()
/*表达式分析*/
{
string op, arg1, arg2, result;
if(lexRes[sym].first == "plus" || lexRes[sym].first == "minus"){
advance();
}
arg1 = T();
while(lexRes[sym].first == "plus" || lexRes[sym].first == "minus"){
op = lexRes[sym].second;
advance();
arg2 = T();
result = newT();
emit(op, arg1, arg2, result);
arg1 = result;
}
return arg1;
}
/**算数表达式的递归下降分析及四元式生成**/
int E_();
int T_();
int F_();
int F_()
{
int arg;
if(lexRes[sym].first == "ident"){
cout << "算数表达式含变量，无法计算\n";
exit(0);
}
else if(lexRes[sym].first == "number"){
arg = atoi(lexRes[sym].second.c_str());
advance();
}
else if(lexRes[sym].first == "lparen"){
advance();
arg = E_();
if(lexRes[sym].first == "rparen"){
advance();
}
else{
cout << "ERROR!未能匹配右括号！语法错误\n";
exit(0);
}
}
return arg;
}
int T_()
/*项分析*/
{
string op;
int arg1, arg2, result;
arg1 = F_();
while(lexRes[sym].first == "times" || lexRes[sym].first == "slash"){
op = lexRes[sym].second;
advance();
arg2 = F_();
if(op == "*"){
result = arg1 * arg2;
arg1 = result;
}
else{
if(arg2 != 0){
result = arg1 / arg2;
arg1 = result;
}
else {
cout << "除数为0，出错！\n";
exit(0);
}
}
}
return arg1;
}
int E_()
/*表达式分析*/
{
string op;
int arg1, arg2, result;
if(lexRes[sym].first == "plus" || lexRes[sym].first == "minus"){
advance();
}
arg1 = T_();
while(lexRes[sym].first == "plus" || lexRes[sym].first == "minus"){
op = lexRes[sym].second;
advance();
arg2 = T_();
if(op == "+"){
result = arg1 + arg2;
arg1 = result;
}
else{
result = arg1 - arg2;
arg1 = result;
}
}
return arg1;
}
int main()
{
lexical();
if(lexRes[0].first == "number"){
cout << E_();
}
else{
E();
for(int i=0; i<quaI; i++){
cout<<‘(‘<<quad[i].op<<‘,‘<<quad[i].arg1<<‘,‘<<quad[i].arg2<<‘,‘<<quad[i].result<<‘)‘<<endl;
}
}
return 0;
}
标签：判断 exit git bit containe ref iterator ide its
原文地址：https://www.cnblogs.com/hesse-summer/p/12903005.html
