added double jump and sitting state

term1/seminar05_iterators/04_is_identifier/main.cpp

@@ -0,0 +1,22 @@
+#include <iostream>
+#include <algorithm>
+#include <string>
+#include <string_view>
+#include <cctype>
+
+using std::cout, std::endl, std::string, std::string_view;
+
+bool isIdentifier(string_view sv) {
+    bool is = true;
+    if (!(std::isalpha(sv[0]) || sv[0] == '_'))
+            return false;
+    if (std::all_of(sv.begin(), sv.end(), [](const char c){ return isalpha(c) || isdigit(c) || c == '_' ;}))
+            return true;
+    return false;
+}
+
+int main() {
+    string s;
+    getline(std::cin, s);
+    cout << isIdentifier(s) << endl;
+}