how to find the length of an string in c 2b 2b

1str.length();

1#include<iostream>
2#include<cstring>
3using namespace std;
4main() {
5   string myStr = "This is a sample string";
6   char myStrChar[] = "This is a sample string";
7   cout << "String length using string::length() function: " << myStr.length() <<endl;
8   cout << "String length using string::size() function: " << myStr.size() <<endl;
9   cout << "String length using strlen() function for c like string: " << strlen(myStrChar) <<endl;
10   cout << "String length using while loop: ";
11   char *ch = myStrChar;
12   int count = 0;
13   while(*ch != '\0'){
14      count++;
15      ch++;
16   }
17   cout << count << endl;
18   cout << "String length using for loop: ";
19   count = 0;
20   for(int i = 0; myStrChar[i] != '\0'; i++){
21      count++;
22   }
23   cout << count;
24}