#include <iostream>
#include <algorithm>
 
bool ok(const std::string &input) {
    return std::find_if_not( 
        input.begin(), //from beginning
        input.end(), //to end
        isalpha //check for non-alpha characters
    ) == input.end();
}
 
int main() {
    std::cout <<
        ok("abc") << '\n' <<
        ok("123") << '\n' <<
        ok("1.4") << '\n' <<
        ok("abc8def") << '\n' <<
        ok("My name is Chris.");
}