Question

For our assignment we have to code a program in C, but it says not to use external variables in the program. Does this mean variables in other files brought into the main code, or am I unable to use variables in the same file if they’re not in the same function? (ie: could I pass a value into a function as an argument and have it return a value that may have to do with a variable in that function and set the return value equal to something, or is that using external variables?)

I’ve Googled around but it’s not exactly clear, and I want to make sure, as this is rather important.

Answer 1

Just to be sure, I’d make all my variables part of a function, and either pass them as parameters or return them from the functions.

There are at least two interpretations of external variables.

First off, we have the extern keyword, which basically symbolizes what you would call a global variable. It’s a variable declared in multiple translation unit, but it only exists in one place in memory. It is initialized in a single file and all subsequent changes affect every scope the variable is used in:

//globals.cpp
int x = 1337;

//main.cpp
extern int x;

int main()
{
   //x is 1337 here
   return 0;
}

The second meaning could be a variable that is declared and defined in class scope, but not used as extern. However, you could consider it external to the methods.

//main.cpp
int x = 1337; //is this external?
              //could be, remove it just to be safe

int main()
{
   return 0;
}