Difference between open subroutine and closed subroutine?

Answer 1

A closed subroutine is a normal unit like a function in C or a method in Java. When a closed subroutine is called, the program branches to the file/section of code, executes, and then returns to the line after the calling line.

For example, if you had the following code in Java:

main(...) {

int a = 1;

int b = 4;

multiply(1,4);

System.out.println("done!");

}

multiply(int a, int b) {

int answer = 0;

for(int i = 0; i < 4; i++)

answer*=a;

return answer;

}

Over here, the main method executes until it reaches multiply(1,4) and then jumps to the function (declared below main) and executes that. After it finishes executing multiple, it returns to the line after the function call, which in our case is System.out.println, and executes that.

An open subroutine is a subroutine that adds the instruction to the already existing block of code. That is, it replaces the one line call with the entire set of instructions.

For example, if you had the following code:

start

save 1 in a

save 4 in b

multiply a b-times

end

The command "multiply a b-times" is an open subroutine because the command will add lines at compile time to the existing code to return the following (this is best understood when thinking of the code as machine code):

(translated from machine code)

start

save 1 in a

save 2 in b

ADDED CODE

save a * a in c

save c * a in d

save d * a in e

return e

end

As you can see, the "multiply" command has been replaced with the entire set of instructions (under ADDED CODE).

In short, an open subroutine adds lines to your main code while a closed subroutine is code stored in a separate block of code. Both subroutines are called with a single line of code.