Newbie help (in C) details inside - c

Question

first of all I am a complete programming newbie, so I am sorry if there is something that does this really easily and I don't know of it, it is in no way my intention to be dumb.
[Also, sorry the programs are in spanish but I don't think the printf's really affect the whole logic thing.
Anyhow:
I made a program that evaluated a number and then got it as near as possible to the closest multiple of three, then I did the same for 5:
//cambia un numero al multiplo de 3 mas cercano
#include <stdio.h>
#include <stdlib.h>
int main(){
int a;
printf("Escribe el numero que deseas redondear: ");
scanf(" %d", &a);
while(a%3 != 0){
--a;
if (a%3 == 0)
break;
a++;
a++;
}
printf("El multiplo de 3 mas cercano es: %d\n", a);
}
//cambia un numero al multiplo de 5 mas cercano
#include <stdio.h>
#include <stdlib.h>
int main(){
int a;
printf("Escribe el numero que deseas redondear: ");
scanf(" %d", &a);
while(a%5 != 0){
--a;
if (a%5 == 0)
break;
--a;
if (a%5 == 0)
break;
a++;
a++;
a++;
if (a%5 == 0)
break;
a++;
if (a%5 == 0)
break;
if (a%5 == 0)
break;
a++;
}
printf("El multiplo de 5 mas cercano es: %d\n", a);
}
Now I want to write a program that does the same, but takes the number of the multiple from the user. I wrote this:
//cambia un numero al multiplo de n (input) más cercano
#include <stdio.h>
#include <stdlib.h>
int main(){
int a, n;
printf("Escribe el numero que deseas redondear: ");
scanf(" %d", &a);
printf("Escribe el numero base para redondear: ");
scanf(" %d", &n);
for(a, n; a%n != 0; a++);
printf("El multiplo de %d mas cercano (A la derecha) es: %d\n",n, a);
}
But of course this only makes it as near as possible from the right, and I don't know how (With n cases) to make it go to the closest number. The idea is this:
5 6 7 8 9 10
If we want it to go to the closest multiple of 5 and the input is 6-7 then it goes to 5, because that is the closest multiple of 5. If the input is 8-9 then it sends it to 10. The idea is always getting to the "closest" number. But I don't really see how to do it. Any help would be greatly appreciated.
If you could alternatively post the help in Java that would be more than sufficient as well. Since I know a bit java as well.
Thanks!

Answer 1

The classic way to do this is divide, round, multiply.