try using code tags on future posts heres a slightly edited version, its not much different, but cleaned i cleaned it up a little bit made it a little easier to read. i dont really know anything about conio.h, but i assume clrscr and getch are both found in it. i also doubt thats your issue, but i dont see anything wrong with the loops which is usually why a program will print endless numbers.
EDIT: not sure if this is it but after thinking it through you add to j and k one extra time. so in your print loops do as i do, j-1 and k-1
#include<stdio.h>
#include<conio.h>
void main(){
int a[12],b[12],c[12],i,j=0,k=0;
clrscr();
printf("Enter 12 numbers\n");
for(i=0;i<12;i++){
scanf("%d",&a[i]);
if((a[i]%2)==0){
b[j]=a[i];
j++;
}
else{
c[k]=a[i];
k++;
}
}
printf("The even numbers are\n");
for(i=0;i<j-1;i++){
printf("%d\n",b[i]);
}
printf("The odd numbers are\n");
for(i=0;i<k-1;i++){
printf("%d\n",c[i]);
}
}