#include <iostream>

using namespace std;

int main()
{
    char arr[] = "grepper";
    cout << sizeof(arr) << endl;
    return 0;
    //    keep it in mind that character arrays have length of one more than your characters because last one is for \0 to show that word has ended
}

char* example = "Lorem ipsum dolor sit amet";
int length = strlen(example);
std::cout << length << '\n'; // 26

Instead of sizeof() for finding the length of strings or character 
arrays, just use strlen(string_name) with the header file
#include <cstring>   
it's easier.