20250628 15:00 Array passing

  

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1. Passing Array Elements — One at a Time!

You can pass one box (element) from the array to a function:

Call by Value:

display(marks[i]);  // just sending the value

void display(int m) {
   printf("%d", m);  // m is just a copy
}

You’re giving the function a photocopy of the value. It can't change the original. 

Call by Reference:

disp(&marks[i]);  // sending the address

void disp(int *n) {
   printf("%d", *n);  // dereference and print the real thing!
}

You’re giving the function a key to the real box (memory address). 

2. Passing the Whole Array to a Function

Why send elements one by one when you can send the whole army? 

int num[] = {24, 34, 12, 44, 56, 17};
display(num, 6);  // OR display(&num[0], 6);

void display(int *j, int n) {
  for (int i = 0; i < n; i++) {
    printf("element = %d\n", *j);
    j++;  // move to next soldier
  }
}

Boom! You just passed the entire array using its base address.

3. Pointers + Arrays = Besties!

Pointers and arrays are like twins :

• num[i] is the same as *(num + i)

• Arrays live in contiguous memory (next to each other)

4. Pointer Magic Show

int num[] = {24, 34, 12, 44, 56, 17};
int *j = &num[0];

for (int i = 0; i < 6; i++) {
  printf("address = %u, element = %d\n", j, *j);
  j++;
}

Every time you do j++, it jumps to the next element (2 bytes ahead for int). It’s like hopping from box to box! 

Pointers Can Fight (And Compare!)

int *j = &arr[4];
int *k = arr + 4;

if (j == k)
  printf("Same location!");

Yes, you can compare pointers. But beware:
Don’t try pointer + pointer
Don’t multiply or divide them
It’ll confuse poor 'C' 

So, When to Use What?

Situation	Use This
Access in fixed order	Use pointers
Access randomly or complex logic	Use subscripts
Want speed?	Pointers zoom!