2d array in c dynamic

//Using Pointer to Pointers
#include <stdio.h> 
#include <stdlib.h> 
  
int main() 
{ 
    int r = 3, c = 4, i, j, count; 
  
    int **arr = (int **)malloc(r * sizeof(int *)); 
    for (i=0; i<r; i++) 
         arr[i] = (int *)malloc(c * sizeof(int)); 
  
    // Note that arr[i][j] is same as *(*(arr+i)+j) 
    count = 0; 
    for (i = 0; i <  r; i++) 
      for (j = 0; j < c; j++) 
         arr[i][j] = ++count;  // OR *(*(arr+i)+j) = ++count 
  
    for (i = 0; i <  r; i++) 
      for (j = 0; j < c; j++) 
         printf("%d ", arr[i][j]); 
  
   /* Code for further processing and free the  
      dynamically allocated memory */
  
   return 0; 
} 

char *x;  // Memory locations pointed to by x contain 'char'
char **y; // Memory locations pointed to by y contain 'char*'

x = (char*)malloc(sizeof(char) * 100);   // 100 'char'
y = (char**)malloc(sizeof(char*) * 100); // 100 'char*'

// below is incorrect:
y = (char**)malloc(sizeof(char) * 50 * 50);
// 2500 'char' not 50 'char*' pointing to 50 'char'

#include <stdio.h> 
#include <stdlib.h> 
  
int main() 
{ 
    int r = 3, c = 4; 
    int *arr = (int *)malloc(r * c * sizeof(int)); 
  
    int i, j, count = 0; 
    for (i = 0; i <  r; i++) 
      for (j = 0; j < c; j++) 
         *(arr + i*c + j) = ++count; 
  
    for (i = 0; i <  r; i++) 
      for (j = 0; j < c; j++) 
         printf("%d ", *(arr + i*c + j)); 
  
   /* Code for further processing and free the  
      dynamically allocated memory */
    
   return 0; 
}