Why do you specify the size when using malloc in C?

Question

Take the following code :

int *p = malloc(2 * sizeof *p);

p[0] = 10;  //Using the two spaces I
p[1] = 20;  //allocated with malloc before.

p[2] = 30;  //U         


        

Answer 1

Do :

int *p = malloc(2 * sizeof(*p)); // wrong (if type is something greater than a machine word)

[type] *p = malloc(2 * sizeof([type])); // right.