The subsequent relies on what I believe is true - but there is no guarantee that I did not misunderstood something. If you feel that there is something not correct below, please feel free to contact me (42 login name: reciak). Any corrections are appreciated.

The enumeration is just for easier reference when communicating with other human beings.

1. Why should libft.h be included in all *.c files although the compiler should work even without doing so?
   It is less error prone:

   • When file.c gets compiled to file.o the compiler will notice a type mismatch between prototype and function definition. --> A danger less that the linker will create a wrongly assembled program producing undefined behavior.

2. Why do functions like

   int isalnum(int c);
   int isalpha(int c);

   expect an integer and not an unsigned char?

   When taking the following into account

   cat /usr/include/stdio.h | grep -B 2 -A 4 "#define.*EOF"
   

   the answer is contained in the man page for isalpha:

   These  functions  check  whether c, which must have the value of an unsigned char or EOF,
   

   Assumed Historical background: Before Unicode started ruling, the original ASCII set (values 0,... 127), using only 7 bits of the 8 ones available in a char variable, used to be complemented in different ways, depending on the laguage in use. To see the effect run the following C Programm in two different Terminal encoding settings, e.g. once in UTF-8 (Unicode Transformation Format - 8-bit) and once in IBM862 (Hebrew - one choice of many extended ASCII codes)

   #include <stdio.h>
   
   int main()
   {
     unsigned char c;
   
     c=0;
     while (c < 255)
     {
       printf("%hhu: %c \n", c, c);    
       c++;
     }
     return 0;
   }

   I assume that isalpha(128) (with 128 standing for the first hebrew letter "ALEPH" in the above Hebrew locale) should return 1 / true if systemwide such an old character encoding would be active.

3. What is the meaning the options r, c and s in ar -rcs?

   • nm -s libft.a prints the symbol table.