C language | Pointer

Compile and execute a C program on Apple m1:

gcc

gcc pointer.c -mcpu=apple-m1 -o output.out && ./output.out

g++

g++ pointer.c -mcpu=apple-m1 -o output.out && ./output.out # g++ way

Basic

int var = 5;
int a = 500;
int *pointerToVar  ;

pointerToVar = &var ; // reference

printf("var: %d\n", var); // var's content
printf("var: %p\n", pointerToVar); // pointerToVar's content which is an address

printf("var: %d \n", *pointerToVar); // dereference pointerToVar

Function’s getting the address of a variable scoped inside another stack frame

#include <stdio.h>

void foo(int *a)
{
  *a = 10;
  printf("a content inside foo: %d\n", *a);
}

void foo2(int a)
{
  a = 10;
  printf("a content inside foo: %d\n", a);
}

int main()
{
  int a = 5;

  int *pointerToA;

  pointerToA = &a; // reference

  printf("a content inside main: %d\n", a);

  foo(pointerToA);
  printf("a content inside main: %d\n", a);

  return 0;
}

Pointer arithmetic with 1D array

#include <stdio.h>

void foo(int arr[])
{
  for (int i = 0; i < 4; i += 1)
  {
    arr[i] = 100;
  }
}

void printArray(int *arr)
{
  for (int i = 0; i < 4; i += 1)
  {
    printf("%dth index item: %d\n", i, *(arr + i));
  }
}

int main()
{
  int arr[] = {30, 30, 35, 15};
  printArray(arr);
  // the name arr refers to the first item's address
  printf("3rd index's address: %d\n", &arr[3]); // 3rd index's address

  printf("3rd index's content: %d\n", arr[3]);
  printf("3rd index's content: %d\n", *(arr + 3));

  foo(arr);

  for (int i = 0; i < 4; i += 1)
  {
    printf("%d\n", arr[i]);
  }

  return 0;
}

Multilevel pointer

#include <stdio.h>

void printArray(int *arr)
{
    for (int i = 0; i < 4; i += 1)
    {
        printf("%dth index item: %d\n", i, *(arr + i));
    }
}

int main()
{
    int arr[] = {30, 30, 35, 15};
    int a = 10;
    int *pointerToA = &a;
    int **pointerToPointerToA = &pointerToA;
    int ***pointerToPointerToPointerToA = &pointerToPointerToA;
    int ****pointerToPointerToPointerToPointerToA = &pointerToPointerToPointerToA;

    printf("Original: %d\n", a);
    printf("De: %d\n", *pointerToA);
    printf("De: %d\n", **pointerToPointerToA);
    printf("De: %d\n", ***pointerToPointerToPointerToA);
    printf("De: %d\n", ****pointerToPointerToPointerToPointerToA);

    return 0;
}

Pointer arithmetic with 2D array

#include <stdio.h>

void printArray(int *arr)
{
    for (int i = 0; i < 4; i += 1)
    {
        printf("%dth index item: %d\n", i, *(arr + i));
    }
}

int main()
{
    int arr[][4] = {
        {30, 60, 35, 15}, // pointerToArr + 0
        {10, 99, 88, 55}, // pointerToArr + 1
        {40, 559, 22, 25} // pointerToArr + 2
    };

    int **pointerToArr = arr;
    for (int row = 0; row < 3; row += 1)
    {
        // printf("%d\n", arr + row);
        for (int col = 0; col < 4; col += 1)
        {
            printf("%d ", *(*(arr + row) + col));
        }
        printf("\n");
    }

    return 0;
}