Problems 3
  1. Theory
    1. How are parameters to functions passed in the C-language, according to the pass-by-value or the pass-by-reference strategy? And what does that mean?
    2. What will the following program print out? 
      #include<stdio.h>
void f(int i){i=0;}
int main(){
	int i=1; f(i); printf("i=%i\n",i);
	return 0; }
    3. What will the following program print out? 
      #include<stdio.h>
void f(int* i){*i=0;}
int main(){
	int i=1; f(&i); printf("i=%i\n",i);
	return 0; }
    4. What will the following program print out? 
      #include<stdio.h>
void f(int* i){i=NULL;}
int main(){
	int i=1; f(&i); printf("i=%i\n",i);
	return 0; }
    5. If you pass an array to a subroutine with the signature void do_something_with_an_array(int a[]); – is it the copy of the array that is passed, or only a copy of the pointer to the first element of the array?
    6. Do arrays in C know their sizes? Hint: the answer "no" is safe, although the question is actually a bit more subtle, see using sizeof with arrays.
    7. At which stage—compilation or execution of the program—is the memory for the following arrays allocated? And which of these arrays "know" their sizes in the scope where they are declared? 
      int a[] = {0,1,2,3,4};
int b[5];
int n = (double)rand()/RAND_MAX*10+1;
int c[n];
int *d=(int*)malloc(n*sizeof(int));
    8. If you pass these arrays to our do_something_with_an_array subroutine, will it be possible to determine the sizes of the arrays inside the subroutine?
    9. If you declare an array as int a[5]; and then try a[7]=1; what will happen? Hint: Segmentation fault / causes.
    10. If you declare a static/variable-length/dynamic array inside a function, can the function return it?
    11. What will the following C-program print? 
      #include<stdio.h>
int i=2; /* file scope */
void f(){printf("i=%i\n",i);}
int main(){
	int i=1; /* function scope */
	{
		int i=0; /* block scope */
		printf("i=%i\n",i);
	}
	printf("i=%i\n",i);
	f();
	return 0; }
  2. Practice
    1. Write a set of functions to deal with 3D vectors that are represented by size-3 double arrays. The signatures should be like 
      void vector_add(double v[], double u[]); /* v+=u */
void vector_subtract(double v[], double u[]); /* v-=u */
void vector_scale(double v[], double a); /* v=a*v */
void cross_product(double v1[], double v2[], double v[]); /* v = v1 x v2 */
double dot_product(double v1[], double v2[]); /* returns v1.v2 */
double vector_norm(double v[]); /* returns |v| */
void vector_print(double v[]); /* prints the components of the vector */
void vector_set(double v[], double v_1, double v_2, double v_3); /* v={v_1,v_2,v_3} */
void vector_set_zero(double v[]); /* v=0 */
void vector_set_basis(double v[], int k); /* v_{k}=1, v_{i!=k}=0 */
int vector_equal(double v[], double u[]); /* returns 1 if v==u, 0 otherwise */
      Hint: something like

      void vector_add(double v[], double u[]){ for(int i=0;i<3;i++) v[i]+=u[i]; return;}

    2. Write a main program that calls and tests your functions. Hint: something like 
      double v[]={1,2,3}, u[]={3,2,1}, r[]={4,4,4};
vector_add(v,u);
if( vector_equal(v,r) ) printf("test 'add' passed :) \n");
else printf("test 'add' failed :( \n");