how malloc allocate memory to a program code example

Example 1: allocate memory c

// Use malloc to allocate memory
ptr = (castType*) malloc(size);
int *exampl = (int*) malloc(sizeof(int));
// Use calloc to allocate and inizialize n contiguous blocks of memory
ptr = (castType*) calloc(n, size);
char *exampl = (char*) calloc(20, sizeof(char));

Example 2: free in c

the C library function void free(void *ptr) 
  deallocates the memory previously allocated by a call to calloc, malloc, or realloc.