STRLEN()

this function counts the number of characters before the null terminator \0. the returned count doesn't including the null terminator

int strlen(char *s);

#include <stdio.h>  // printf
#include <string.h> // strlen

void main (void)
{
    char string_array[] = "This is a string";

    printf("strlen(string_array) is %ld\n", strlen(string_array));
    printf("sizeof(string_array) is %ld\n", sizeof(string_array));
}

 * the strlen function returns the length of the string, in characters (or bytes), not 
   including the terminating NULL byte. The sizeof operator returns the number of bytes
   the array consumes in memory. Ultimately, when working with strings the number of 
   bytes consumed by the array will be one greater than string length as it takes into 
   account the full size of the array to include the terminating NULL byte.

#manually counting the length of a string

void printLength(char str[]) {     //since arrays and pointers are related - confirmed can use char *str as parameter instead of char str[]
    int length = 0;

    // Calculate the string length manually
    while (str[length] != '\0') {
        length++;
    }
}

 * this looks like how the strlen() works internally!