Question

In a C program, how does function call by value work, and how does call by reference work, and how do you return a value?

Answer 1

Call by value

void foo(int c){
    c=5; //5 is assigned to a copy of c
}

Call it like this:

int c=4;
foo(c);
//c is still 4 here.

Call by reference: pass a pointer. References exist in c++

void foo(int* c){
    *c=5; //5 is assigned to  c
}

Call it like this:

int c=0;
foo(&c);
//c is 5 here.

Return value

int foo(){
    int c=4;
     return c;//A copy of C is returned
}

Return through arguments

   int foo(int* errcode){

       *errcode = OK;

        return some_calculation
   }