I don't understand multi dimensional arrays using pointers and pointers in arrays

[Xenon02]

I tried to understand these two codes :

int *pv = (int*) malloc(5 * sizeof(int));
    for(int i=0; i<5; i++) {
        pv[i] = i+1;
    }

This is a one dimensional array.
And I am confused of how malloc works and why it is also a pointer (int *) ?? Because I had more simple examples such as this one :

#include 
int main() {

  int x[5] = {1, 2, 3, 4, 5};
  int* ptr;

  // ptr is assigned the address of the third element
  ptr = &x[2]; 

  printf("*ptr = %d \n", *ptr);   // 3
  printf("*(ptr+1) = %d \n", *(ptr+1)); // 4
  printf("*(ptr-1) = %d", *(ptr-1));  // 2

  return 0;
}

The pointer here ptr is pointing at the address of x[2] which is written as &x[2]. So why now the pointer points at the malloc which is also a pointer ?

In the Two-dimensional arrays I saw this example :

int rows = 2;
    int columns = 5;
    int **matrix = (int **) malloc(rows * sizeof(int *));
    matrix[0] = (int *) malloc(rows * columns * sizeof(int));
    for (int i = 1; i < rows; i++)
        matrix[i] = matrix[0] + i * columns;

I don't understand what is written here. Why matrix is used twice ? Once as **matrix and one as matrix[0] ? And why **matrix changed into matrix[0] ?

Isn't **matrix the same as matrix[][] ??

Like in this example :

#include 
int main() {

  int i, x[6], sum = 0;

  printf("Enter 6 numbers: ");

  for(i = 0; i < 6; ++i) {
  // Equivalent to scanf("%d", &x[i]);
      scanf("%d", x+i);

  // Equivalent to sum += x[i]
      sum += *(x+i);
  }

  printf("Sum = %d", sum);

  return 0;
}

Also I don't understand arrays of pointers like here :

#include 
 
int main()
{
 
    char* arr[3] = { "geek", "Geeks", "Geeksfor" };
 
    for (int i = 0; i < 3; i++) {
        printf("%s\n", arr[i]);
    }
 
    return 0;
}

the arrays is in char and char can only store a single character so how ? arr[0] shows geek and not just a letter "g" ? And how does the *arr know what is the address of "geek" ?

This example shows :

#include 
 
int main()
{
    // declaring some temp variables
    int var1 = 10;
    int var2 = 20;
    int var3 = 30;
 
    // array of pointers to integers
    int* ptr_arr[3] = { &var1, &var2, &var3 };
 
    // traversing using loop
    for (int i = 0; i < 3; i++) {
        printf("Value of var%d: %d\tAddress: %p\n", i + 1, *ptr_arr[i], ptr_arr[i]);
    }
 
    return 0;
}

That in the arrays of pointer I have to put the address of the variable but in char *arr I just put a string and not an addres like above (like &var instead in char arr there is "geek" and not address of this string).