->
---> b
---> 1 | 1个
假设先启动a或b,然后再启动1。 a或b之后的1无关紧要。例如:a1,b1,b111111,a111
我输入的所有内容均无效,但这应该是有效的:a1,b1,b111111,a111
/*
<S> --> <A><B>
<A> ---> a | b
<B> ---> 1 | 1 <B>
It suppose to be vaild for example: a1, b1, b111111, a111
*/
#include <iostream>
#include<stdlib.h> // for the exit(1) function
using namespace std;
char text[100];
char ToBeChecked;
char lexical(); //identify the characters
void SProd();
void AProd();
void BProd();
int main()
{
cout<<"Enter a string(max. 100 characters"<<endl;
cin>>text;
ToBeChecked = lexical(); //identify the character; find the first letter and give it to ToBeChecked
SProd();
if(ToBeChecked = '\0')
cout<<"Valid"<<endl;
else
cout<<"Invalid"<<endl;
cin.get();
return 0;
}
char lexical()
{
static int index = -1; //a memory box named index with a value of -1; is static so it won't change.
//is -1 because -1 to 1 is 0; everytime move on to next one
index++; //update index
return text[index]; //return the value of index
}
//<S> --> <A> <B>
void SProd()
{
AProd();
BProd();
}
//<A> ---> a | b
void AProd()
{
if(ToBeChecked == 'a'){
ToBeChecked = lexical();
}
else
{
if(ToBeChecked == 'b'){
ToBeChecked = lexical();
}
}
}
//<B> ---> 1 | 1 <B>
void BProd()
{
if(ToBeChecked != '1')
{
cout<<"Invalid"<<endl;
exit(1);
}
else
while (ToBeChecked == '1')
ToBeChecked = lexical();
}
最佳答案
仔细看这条线
if(ToBeChecked = '\0')
它是做什么的,为什么那不是您想要的?
关于c++ - 解析器帮助程序不起作用,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/5161389/