Is it "OK" to leave out the variable `n` in the "capitalize" walkthough from pset2?

Question

I normally watch the video and then switch to my editor program and rebuild it out of memory following my logic and the tools I just learned.

So I programmed it a little bit different and wondered if it was against logic or style definitions to leave out the variable n, directly jump to the condition part and compare i to strlen(s)

Original:

    #include <cs50.h>
    #include <stdio.h>
    #include <string.h>

    int main (void)
    {
        printf("Input\n");
        string s = GetString(); 

      for (int i = 0, n = strlen(s); i < n; ++i)

        {
            if (s[i] >= 'a' && s[i] <= 'z')
            {
                printf("%c", s[i] - ('a' - 'A'));
            }
        }
        printf("\n");
     }

My approach:

      for (int i = 0 ; i < strlen(s); ++i)

Answer 1

Both are valid, but they have a big difference. As is explained in the video, the main difference is that in your approach everytime the loop runs the condition it has to check the length of s, since in the other approach, that length is stored into a variable at the beginning of the loop so you don't need to call the length() function each time.

Your approach:

Store 0 in the variable i
Check if i is less than (take the length of s)
    if so printf("%c", s[i] - ('a' - 'A'));
Loop
Check if i is less than (take the length of s)
    if so printf("%c", s[i] - ('a' - 'A'));
Loop
Check if i is less than (take the length of s)
    if so printf("%c", s[i] - ('a' - 'A'));
Loop ...

While the other approach is:

Store 0 in the variable i
Store (take the length of s) in the variable n
Check if i is less than n
    if so printf("%c", s[i] - ('a' - 'A'));
Loop
Check if i is less than n
    if so printf("%c", s[i] - ('a' - 'A'));
Loop
Check if i is less than n
    if so printf("%c", s[i] - ('a' - 'A'));
Loop ...

So, doing it this way, you save time calling the lenght() function just once, while in your approach you are calling it in every iteration.