Why this while loop executes twice before asking for name - c++

Question

I have a function which validates a user's first and last name. However, the while loop executes twice, and I can't find out why.... any help
string getName()
{
string name = "";
bool stop = false;
string::iterator it;
while(!stop)//name validation loop
{
cout << "enter name: ";
getline(cin, name);
for(it = name.begin(); it < name.end(); it++)
{
if(tolower(*it) > 'z' || tolower(*it) < 'a' && tolower(*it) != ' ')
{
cout << "Error, only letters! \n";
break;
}
if(it == name.end()-1) { stop = true; }
}
cout << "here\n";
}
return name;
}

Answer 1

It may happen if there is still some newspace character in cin buffer. std::ws extracts white spaces like newline character, space, tabulator from stream before right text. Try that:
string getName()
{
string name = "";
bool stop = false;
string::iterator it;
while(!stop)//name validation loop
{
cout << "enter name: ";
std::cin >> std::ws; // <--- drop whitespaces
getline(cin, name);
for(it = name.begin(); it < name.end(); it++)
{
if(tolower(*it) > 'z' || tolower(*it) < 'a' && tolower(*it) != ' ')
{
cout << "Error, only letters! \n";
break;
}
if(it == name.end()-1) { stop = true; }
}
cout << "here\n";
}
return name;
}

Answer 2

There are a few problems with your loop and this is how I'd rewrite it, keeping it as similar to your implementation as possible:
string getName()
{
bool stop;
string name;
string::iterator it;
do {
stop = true;
cout << "enter name: ";
getline(cin, name);
for(it = name.begin(); it < name.end(); it++)
{
if( (tolower(*it) > 'z' || tolower(*it) < 'a') && tolower(*it) != ' ' )
{
cout << "Error, only letters! \n";
stop = false;
break;
}
}
cout << "here\n";
} while (!stop);
return name;
}
With what you had here:
if(tolower(*it) > 'z' || tolower(*it) < 'a' && tolower(*it) != ' ')
Due to && having higher precedence, it equates to:
if(tolower(*it) > 'z' ||(tolower(*it) < 'a' && tolower(*it) != ' '))
which is not what you want.
EDIT: since ' ' (space) is < 'a' your code won't actually cause problems, but I'm not sure you did it like that on purpose.
I also don't like this: if(it == name.end()-1) { stop = true; }, and a do...while loop is better suited.
EDIT: You might also want to add a check for empty input (all whitespace), since that would seem an invalid name.
EDIT(again): Loki's right, you must have junk on the input stream before calling getName. You can use Mścisław's solution or cin.ignore().