added double jump and sitting state

term1/seminar01_overload/04_count_letters/count_letters.cpp

@@ -0,0 +1,26 @@
+#include <iostream>
+using std::cout, std::endl;
+
+void count_letters(char str[], int& n_letters, int& n_digits, int& n_other) {
+        while (*str) {
+            if (*str >= 'a' && *str <= 'z' || *str >= 'A' && *str <= 'Z') {
+                n_letters += 1;
+            }
+            else if (*str >= '0' && *str <= '9') {
+                n_digits += 1;
+            }
+            else {
+                n_other += 1;
+            }
+            str += 1;
+        }
+}
+
+int main() {
+    int n_letters = 0, n_digits = 0, n_other = 0;
+    
+    char s[] = "1n!2y#3a$";
+    count_letters(s, n_letters, n_digits, n_other);
+
+    cout << "letters: " << n_letters << endl << "digits: " << n_digits << endl << "n_other: " << n_other << endl;
+}