CareerCup

static StringBuffer intToString(int n){
    StringBuffer buf = new StringBuffer();
    
    if(n == 0){
        buf.append(0);
    }else{
        while(n > 0){
            buf.insert(0,n%10 );
            n/=10;
        }
    }
    return buf;
}

static String floatToString(double n){
    boolean nLessThanOne = (n < 1.0);
    if(nLessThanOne)
        n+=1;
    
    double floatPt = n;

    while(floatPt%10 > 0){
        floatPt*=10;
    }
    floatPt/=10;

    StringBuffer buf = intToString((int)floatPt);
    int floatPos = (int)floor(log10(n));

    if(nLessThanOne){
        buf.deleteCharAt(0);
        buf.insert(0, ".");
    }else{
        buf.insert(floatPos+1, ".");
    }

    return buf.toString();
}

The most obvious feature missing from the function is that it does not handle negative numbers but including that is trivial.

this was telephonic or onsite interview question? US/India?

or else we simply can do this

String floattoString(float x)
{
  String y = ""+x;
  return y;

}

long beforeDP = d/1;
double afterDP = d - beforeDP;
StringBuffer sb = new StringBuffer();
if(beforeDP < 1) sb.append(0);
while(beforeDP > 1)
{
   long l = beforeDP % 10;
   beforeDP /= 10;
   sb.append(l);
}
sb.append('.');

long l = afterDP * 10;
while(l != 0)
{
  sb.append(l);
  afterDP *= 10.0;
  afterDP -= l;
  l = afterDP * 10;
}
System.out.println(sb);