Decimal to Octal number in c

Decimal to Octal number conversion:

Code:
#include<stdio.h>
int main()
{
    int num,i;
    scanf("%d",&num);
    if(num>=0)
    {
        for(i=1;i<=num;i*=8)
        {}
        for(i/=8;i!=1;i/=8)
        {
            printf("%d",num/i);
            num%=i;
        }
        printf("%d",num);
    }
    else
    {
        printf("Can not calculate.\n");
    }
    return 0;
}