How can I write the same function by using exactly one loop

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Java

<pre>static void fun(int x) {
int a, b, c, d;
d = 1;
for (a = 1; a <= x; a++) {
b = a;
c = 1;
while (b > 0) {
c &= b % 2;
b /= 2;
}
d += c;
}
 System.out.println(d);
}

What I have tried:

I have tried to change the while loop into if loop and then after the loop assigns the new values to the variables, I have tried to use continue; but results has been completely different. I have also attempted to get rid of the for loop and increment the a value without a loop but result has been different also.

Posted 13-Apr-19 4:11am

Member 14231773

Updated 13-Apr-19 12:52pm

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CPallini · Answer 1 · 2019-04-13T11:13:00

Solution 2

Java

static void very_fun(int x)
{
  int b = 1, c = 1;
  for (int a = 1; a <= x; a += b)
  {
    ++c;
    b *= 2;
  }
  System.out.println(c);
}

Posted 13-Apr-19 11:13am

CPallini

#realJSOP · Answer 2 · 2019-04-13T04:16:00

Solution 1

What you need is a recursive function.

java recursive functions at DuckDuckGo[^]

Posted 13-Apr-19 4:16am

#realJSOP

Patrice T · Answer 3 · 2019-04-13T12:52:00

Quote:
I have tried to use continue; but results has been completely different.

Trying random changes in code is a bad idea.

Learn to indent properly your code, it show its structure and it helps reading and understanding. It also helps spotting structures mistakes.

C++

static void fun(int x) {
	int a, b, c, d;
	d = 1;
	for (a = 1; a <= x; a++) {
		b = a;
		c = 1;
		while (b > 0) {
			c &= b % 2;
			b /= 2;
		}
		d += c;
	}
	System.out.println(d);
}

Indentation style - Wikipedia[^]

Professional programmer's editors have this feature and others ones such as parenthesis matching and syntax highlighting.
Notepad++ Home[^]
ultraedit[^]

Quote:
How can I write the same function by using exactly one loop

On first reading, it looks like the 2 loops are needed, so if you have to keep it in 1 function, you need to fully understand what is doing this code.

This

C++

c &= b % 2;
b /= 2;

tells that the code is messing with the binary form of b

first thing to do is run the function with x=1, 2, 3, 4 ... 16
note matching results and binary of x

x binary result
  1    1
  2   10
  3   11
...

then you have to find the reason why result change, this understanding may lead to simplify and a loop removal.
Otherwise, CPallini's solution is just magic and you will learn nothing.