这是错误报告error C2065: str undeclared identifier
```c++
#include<stdio.h>
#include<iostream>
#include<string>
using namespace std;
#include<fstream>
#define MAXEXP 20
int input(char *filename,string[]){
ifstream infile(filename,ios::in);
int i=0;
while(!infile.eof()){
getline(infile,str[i]);
i++;
}
infile.close();
return i-1;
}
int main(){
int count;
string a[MAXEXP];
count=input("input.txt",a);
return 0;
}
```