Limit input to alphabet only [a-z, A-Z,SPACE,PERIOD] - c++

Question

I'm trying to limit user input to certain characters only [a-z,A-Z,SPACE,PERIOD], I can't get this function right?!
void setName()
{
char fname[20];
unsigned int ascii_val;
while(ascii_val<65 || ascii_val>90)
{
cout << "First Name: ";
cin.ignore().getline(fname,20);
for(int i=0; i<sizeof(fname); i++)
{
ascii_val = toupper(fname[i]);
if(ascii_val==32 || ascii_val==46 || ascii_val==0) //Exception to allow SPACE and PERIOD
{
ascii_val=65;
};
if(ascii_val<65 || ascii_val>90)
{
cout << "Only Alphabet [a-z,A-Z,SPACE,DOT] Allowed!\n";
break;
}
}
}
newfname = fname;
}

Answer 1

This finally worked! if you think this is not the best solution, post your alternative please.
bool charVerify(string word)
{
for (int i = 0; i < word.size(); i++)
{
int character = toupper(word[i]);
if(character == ' ' || character == '.')
{
character='A';
}
if (character < 'A' || character > 'Z')
{
return false;
}
}
return true;
}
void setFname()
{
string fname;
cout << "Enter Name: ";
getline(std::cin.ignore(),fname);
while(1)
{
if (charVerify(fname))
{
break;
}
else
{
cout << "\tInvalid Input! Only [a-z,A-Z,SPACE,PERIOD]" << endl;
}
cin.clear();
cout << "Enter Name: ";
getline(std::cin.ignore(),fname);
}
firstname = fname;
}