Che problemi hai?
codice:
char *c;
void *p;
double *d;
long int *li;

c = (char *) malloc(sizeof(char)); // 1 carattere
p = (void *) malloc(30); //30 byte
d = (double *) malloc(4 * sizeof(double)) // 4 double
li = (long int *) malloc(1 * sizeof(long int)) // 1 long int