How to check a string if a string has only alphabetical characters in C++

Question

I'm writing a program for an assignment. Part of it is I need to validate a certain string so it only contains alphabetical characters but I can't figure it out. This was a test code I used to attempt to write a validator.

#include <cstring>
#include <iostream>
#include <string>

using namespace std;
bool isValidName(string str);
string str[20];

main() {
  cout << "enter name\n ";
  getline(cin, str[1]);
  isValidName(str[1]);
  cout << isValidName << endl;
  system("pause");
}

bool isValidName(string str) {
  for (int i = 0; i < (int)str.length(); i++) {
    if (!isalpha(str[i])) {
      return false;
      break;
    }
    return true;
    break;
  }
}

It doesn't matter what kind of character I put it, it will always return 1 :o(

(Thanks to Paul Rooney for fixing the indentation)

Answer 1

Another way of writing your validation proc would be:

bool isValidName(const std::string& str) 
{
    return std::all_of(str.begin(), str.end(), isalpha);
}

In your function:

bool isValidName(string str) 
{
    for(int i=0;i<(int)str.length();i++) 
    {
        if (!isalpha(str[i])) 
        {
            return false;
            break;               // breaking here is useless, you've already returned.
        }
        return true;            // this is not in the right spot.  you return true
                                // if the first character is alpha !!
    }

    return true;               // <-- should be here.
}

Proper indentation makes these errors easy to spot.

Answer 2

One of the problems was you were not printing the return of the function, you were printing the the function variable. cout << isValidName << endl; //wrong

you were also already making returning in the first character check, I hope the code below can help you

#include <iostream>
#include <string>
#include <cstring>

using namespace std;
bool isValidName(string str);
string str;

main(){
    cout << "enter name\n ";
    getline(cin, str);
    cout << isValidName(str) << endl;
}

bool isValidName(string str) {
    for(int i=0;i<(int)str.length();i++) {
        if (!isalpha(str[i])) {
            return false;     
        }
    }
    return true;
}

fixed thanks to rooney

Answer 3

Another elegant solution is to use regular expressions to validate your input.

#include <iostream>
#include <string>
#include <regex>

bool isValidName(const std::string& str)
{
    if (std::regex_match(str, std::regex("[[:alpha:]]*")))
        return true;
    return false;
}

int main()
{
    std::string s("aaASd");
    std::cout << isValidName(s) << std::endl;
    std::string s1("ss23d");
    std::cout << isValidName(s1) << std::endl;

    return 0;
}