The same ruslt as required in task The Spy Life, but isn't work.

Question

I wrote this code for task The Spy Life and when I run Test I got the same result as required but I got info that Test crashes. Does anybody know why is this happen?
#include <iostream>
#include <string>
using namespace std;

int main() {
string str;
getline(cin, str);
int len=str.length();
int n=len-1;
for(int i=0; i<=len; i++) {
if (!((str[i]>='a' && str[i]<='z') || (str[i]>='A' && str[i]<='Z') || str[i]==' ')) {
str[i]='\0';
}
}
for(int i=0;i<(len/2);i++)
{
char temp=str[i];
str[i]=str[n];
str[n]=temp;
n=n-1;
}
cout<<str;
return 0;
}

Answer 1

Because you don't remove characters that are not a letter or a space from a string.
You just replacing them with zero chracter.

Declare new string and append only valid characters to it.
And you can iterate a source string in reverse order in the first loop then you don't need the second loop.