#include<stdio.h>
#include<conio.h>
void main(void)
{
int idem=0,n,dv,lc,ktra;
printf("Ban nhap n = ");
scanf("%d",&n);
lc=n%10;
ktra=n;
while(n!=0)
{
dv=n%10;
if(dv>=lc)
lc=dv;
n=n/10;
}
while(ktra!=0)
{
dv=ktra%10;
if(lc==dv)
idem++;
ktra=ktra/10;
}
printf("Ket qua %d",idem);
getch();
}

#include<conio.h>
#include<math.h>
int nguyento(int n)
{
int i;
for (i=2;i<=sqrt(n);i++)
if(n%i==0)
return 0;
return 1;
}
void main()
{
int b,a,i;
printf("\n Nhap a=");
scanf("%d",&a);
while (a!=0)
{
b=a%10;
a=a/10;
if(nguyento(b))
printf("%d ",b);//neu nhap 123456 in ra 1,2,3,5 la so nguyen to thi cau lenh in la the nao?
}
printf("la so nguyen to");
getch();
}