how to use malloc in c

1#include <iostream>
2#include <cstdlib>
3using namespace std;
4
5int main()
6{
7	int *ptr;
8	ptr = (int*) malloc(5*sizeof(int));
9
10	if(!ptr)
11	{
12		cout << "Memory Allocation Failed";
13		exit(1);
14	}
15	cout << "Initializing values..." << endl << endl;
16
17	for (int i=0; i<5; i++)
18	{
19		ptr[i] = i*2+1;
20	}
21	cout << "Initialized values" << endl;
22
23	for (int i=0; i<5; i++)
24	{
25		/* ptr[i] and *(ptr+i) can be used interchangeably */
26		cout << *(ptr+i) << endl;
27	}
28
29	free(ptr);
30	return 0;
31}

1/* malloc example: random string generator*/
2#include <stdio.h>      /* printf, scanf, NULL */
3#include <stdlib.h>     /* malloc, free, rand */
4
5int main ()
6{
7  int i,n;
8  char * buffer;
9
10  printf ("How long do you want the string? ");
11  scanf ("%d", &i);
12
13  buffer = (char*) malloc (i+1);
14  if (buffer==NULL) exit (1);
15
16  for (n=0; n<i; n++)
17    buffer[n]=rand()%26+'a';
18  buffer[i]='\0';
19
20  printf ("Random string: %s\n",buffer);
21  free (buffer);
22
23  return 0;
24}

1#include <stdlib.h>
2
3void *malloc(size_t size);
4
5void exemple(void)
6{
7  char *string;
8  
9  string = malloc(sizeof(char) * 5);
10  if (string == NULL)
11    return;
12  string[0] = 'H';
13  string[1] = 'e';
14  string[2] = 'y';
15  string[3] = '!';
16  string[4] = '\0';
17  printf("%s\n", string);
18  free(string);
19}
20
21/// output : "Hey!"

1int main(int argc, char *argv[])
2{
3    int* memoireAllouee = NULL;
4
5    memoireAllouee = malloc(sizeof(int));
6    if (memoireAllouee == NULL) // Si l'allocation a échoué
7    {
8        exit(0); // On arrête immédiatement le programme
9    }
10
11    // On peut continuer le programme normalement sinon
12
13    return 0;
14}
15

1int* a =(int*)malloc(sizeof(int))

1ptr = (castType*) malloc(size);