Check if string contain only letters - c++

Question

I have a trouble with a search through a string, if I enter a word with only letters, it's work as needs, I though, the code works, but when I add a number in work, the code work also, the question that, is possible to accept only if my var contains only letters, and if it will find a number or symbol, to go at begining of code?
#include <iostream>
#include <string>
#include <cctype>
using namespace std;
int main()
{
label:
string var1 = "";
cout << "Enter a word: ";
cin >> var1;
for (int i = 0; i < var1.size (); i++)
{
int uppercaseCHar = toupper (var1[i]);
if (uppercaseCHar < 'A' || uppercaseCHar > 'Z')
{
goto endloop;
cout << endl;
} else
goto label;
cout << endl;
}
endloop:
cout << "Yout word contains only letters";
}
Output:
Enter a word: work
Enter a word: wro1
Enter a word: 123
Yout word contains only letters

Answer 1

Here is a solution that uses std::all_of:
#include <iostream>
#include <string>
#include <cctype>
#include <algorithm>
int main()
{
bool isAllLetters = false;
do
{
std::string var1;
std::cout << "Enter a word: ";
std::cin >> var1;
// check if all characters are letters
isAllLetters = std::all_of(var1.begin(), var1.end(), [](char ch)
{ return std::isalpha(static_cast<unsigned char>(ch));});
if ( isAllLetters )
std::cout << "Your word contains only letters\n";
else
std::cout << "Your word contains stuff other than letters\n"
} while ( !isAllLetters );
}

Answer 2

Simple and efficient (C++17):
#include <algorithm>
#include <cctype>
#include <string_view>
bool all_of_alpha(std::string_view s)
{
return std::all_of(s.begin(), s.end(), [](unsigned char c) { return std::isalpha(c); });
}

Answer 3

Avoid using goto as it will complicate debugging code in larger program , here's another way :
int main()
{
while (true) {
bool flag = false; // to check for numeric entry
string var1; // not req to initialize
cout << "Enter a word (press exit to end): ";
cin >> var1;
for (int i = 0; i < var1.size(); i++)
{
int uppercaseCHar = toupper(var1[i]);
if (!std::isalpha(uppercaseCHar))
{
flag = true;
break;
}
}
if (var1.compare("exit") == 0) break;
if (flag) {
cout << "Your word contains number";
cout << endl;
}
else
{
cout << "Your word contains only alphabets";
cout << endl;
}
}
}

Answer 4

You can also use regular expressions which will simplify the code further.
#include <iostream>
#include <string>
#include <regex>
using namespace std;
int main () {
regex reg_obj("^[A-Z]+$");
string var;
start_label:
cout << "Enter a word: ";
getline(cin, var);
if(regex_match(var, reg_obj))
goto endlabel;
else goto start_label;
endlabel:
cout << "your word contains only letters\n";
return 0;
};

Answer 5

Allow me to offer a more modern idiomatic version and assuming you only care about detecting alphabetic characters in the ASCII character set.
#include <iostream>
#include <algorithm>
#include <string>
int main()
{
std::string a = "abcdefgh";
std::string b = "abcd3fgh";
std::string c = "abcdefg0";
auto is_alpha = [](unsigned char c){ return std::isalpha(c); };
bool aContainsAlphas = std::all_of(a.begin(), a.end(), is_alpha);
bool bContainsAlphas = std::all_of(b.begin(), b.end(), is_alpha);
bool cContainsAlphas = std::all_of(c.begin(), c.end(), is_alpha);
std::cout << std::boolalpha;
std::cout << "A: " << aContainsAlphas << '\n'; // true
std::cout << "B: " << bContainsAlphas << '\n'; // false
std::cout << "C: " << cContainsAlphas << '\n'; // false
}
This defines a lambda which is passed as an argument to std::all_of, which uses it to test each character:
auto is_alpha = [](unsigned char c){ return std::isalpha(c); };
This invokes is_alpha on each element between a.begin() and a.end(). If the end is reached without any mismatch for is_alpha, then true is returned.
bool aContainsAlphas = std::all_of(a.begin(), a.end(), is_alpha) != a.end();