C++无限循环问题

Question

I am not sure what the issue may be. I added "cout << count;" to the if statements to see why there is no return value 'val'.

But now I see there is an infinite loop occurring.

I'm essentially trying to count how many loops it takes for num = 0.

At first I thought it was num = count being in the loop.

Any suggestions? Thanks in advance.

#include <iostream>
using namespace std;

// hailstone function prototype
int hailstone(int &num);


int main()
{
    int val;

    cout << "Enter integer" << endl;
    cin >> val;

    hailstone(val);

    cout << val << endl;

    return 0;


}

// Pass values by reference to hailstone function header
int hailstone(int &num)
{   

    do
    {
        int count = 0;    

        // If num is even
        // Divide by two
        if(num % 2 == 0)
        {
            num = (num / 2);
            count++;
            cout << count;

        }

        // If num is odd
        // Multiply by 3 and add 1
        else if(num % 2 != 0)
        {
            num = (num * 3) + 1;
            count++;
            cout << count;

        }
    // Assign the number of steps to num
    num = count;

    } while(num > 0);

    // Return the number of steps
    return num;
}

Answer 1

There are a few issues here, but the most pertinent is this line:

// Assign the number of steps to num
num = count;

You're essentially resetting num after you update it based on the rules of the hailstone sequence. Because 'count' is initialized at the start of each loop and then iterated once in either the 'if' or 'else if' block, it is always one. Therefore, at the end of each loop, num is always 1.

Answer 2

Whether you are doing num = num/2; (for even numbers) or num = (num * 3) + 1 (for odd numbers), the number will never become 0 or less . That's why your code runs for infinite time. So you need to change the line while (num > 0); to while(num > 1); inside the function hailstone (maybe it is line number 54). As like as follow:

Old code:

int hailstone(int &num)
{   

do
{
    int count = 0;    

    // If num is even
    // Divide by two
    if(num % 2 == 0)
    {
        num = (num / 2);
        count++;
        cout << count;

    }

    // If num is odd
    // Multiply by 3 and add 1
    else if(num % 2 != 0)
    {
        num = (num * 3) + 1;
        count++;
        cout << count;

    }
// Assign the number of steps to num
num = count;

} while(num > 0); //You need to change this line

// Return the number of steps
return num;
}

New Code:

int hailstone(int &num)
{   

do
{
    int count = 0;    

    // If num is even
    // Divide by two
    if(num % 2 == 0)
    {
        num = (num / 2);
        count++;
        cout << count;

    }

    // If num is odd
    // Multiply by 3 and add 1
    else if(num % 2 != 0)
    {
        num = (num * 3) + 1;
        count++;
        cout << count;

    }
// Assign the number of steps to num
num = count;

} while(num > 1); //Here is the change

// Return the number of steps
return num;
}

Another issue: You declares num = count (in line 52), which will not return the actual value (if your code is for counting number of loops). Example: If the input is 12 than the loop will run for 10 times but your code will print 11 , I don't think this line is required. Return the value of count variable after your do-while loop breaks. Thanks

Answer 3

显然，'if' 或 'else if' 条件将被满足，这将使 count 增加到 1 ，并且分配 num =count 使 num =1 ，so(num>0) 总是 true.so 循环永远继续

Answer 4

do
{
  int count = 0;    

  if (num % 2 == 0)
  {
    num = (num / 2);
    count++;
    cout << count;
  }
  else if(num % 2 != 0)
  {
    num = (num * 3) + 1;
    count++;
    cout << count;
  }

  num = count;

} while (num > 0);