I am unable to find a proper meaning or the purpose of the %lu in C language.
I tried Googling it. I couldn't find a satisfying answer. I have attached the link where the %lu is been used in the program.
char greetings[] = {'H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd', '!', '\0'};
char greetings2[] = "Hello World!";
printf("%lu\n", sizeof(greetings)); // Outputs 13
printf("%lu\n", sizeof(greetings2)); // Outputs 13
https://www.w3schools.com/c/tryc.php?filename=demo_strings_sizeof