info.txt

There are mainly 3 components to a function/variables:-
1) Declarartion:-> no memory is allocated just telling the compiler that 
                   this variable or a function exists. This part is mainly 
                   done in a header file. Which is then included into the c 
                   file when definition or function call might be present.

2) Definition:->   Here the memory is alocated to the variable or a function. 
                   This is done in a .c file

3) FunctionCall:-> Here the function or the variable is called


In C, the extern keyword is primarily used for variables to indicate that the 
variable is defined elsewhere. For functions, including extern is optional and 
doesn't change the linkage behavior. Functions declared in a header file without 
extern still have external linkage by default.


Header File (declaration.h): This is where you declare your variables and 
functions that will be used across multiple source files. The extern keyword tells
the compiler that these variables are declared elsewhere.This prevents the 
compiler from expecting to find the function definition in the current 
translation unit (source file).


Source File (convert.c): Here, you include declaration.h to make use of the 
declarations. You then define (allocate memory for) and initialize the global 
variables sq120_sq64 and sq64_sq120. This ensures that there's only 
one definition of these variables in your entire program.