Thread: nested while-loop + undetermined error

I was working on a problem and able to detect the source. So, I keep isolating until I got the short code that caused me to buzz my head.

Here is the code:

Code:

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
	
	int power=1;
	int i=1;
	int counter=1;
	while (i<=10)
	{
		cout << "i = " << i << endl;
		while (counter<=(10-i))
		{
			power *= 2;
			counter++;
		}
		cout << power << endl;
		i++;
	}
	return 0;
}

If I replaced counter <= i, the program will output correctly

Code:

2
4
8
....
1024

In order to replicate my program, I tweaked it to be counter <= (10-i), then it started to screw up.

Code:

512
512
512
......

I thought this is weird, since I analyzed it this way:
At i=1, j=1, then power = 2
At i=1, j=2, then power = 4
......
At i=1, j = 9, then power = 2^9 = 512
------------------------------------------------
At i=2, similarly, at the end of the inner-loop, j=8, the power should be 256?

Perhaps, I misconcept something??
Any hints will be so useful!
THanks!

thanks!!
When using counter <= i the output will be

Code:

2
4
8
16
...
1024

I'd like to achieve the reverse.
But, thanks, initializing "power" and "counter" inside the outer loop solve the problem.
however, as I understand, variable should be replaced by new values whenever they're re-called, right?
Shouldn't it matter whether you place the initialization out of the outer loop?

Thanks!

however, as I understand, variable should be replaced by new values whenever they're re-called, right?

not true. Variables only change value when you explicitly set it to equal a new value.

you could leave the initialization (and declaration) outside the loop, just that you have to initialize (set) them in each iteration.

hey thanks!
The actual goal for this code is to calculate the sum of all digits of an integer.
I'm sure there's smarter way doing this. Here is what I did (using loops and division/modulus)

1. Input number (of course!)
2. Count how many digits it has (digitCount)
3. The first digit is easy, firstDigit=number/10^(digitCount-1)
4. For these middle digits, I used nested while loops, 2 of them. The last digit is excluded from these loops, however.

Code:

int counter=1;
int part_number;	
while(counter < (digitCount - 1))
	{
		//Need to calcuate power of base 10
		int power=1;
		int counter_power=1;	
		while (counter_power<= (digitCount-counter))
		{
			power = power*10;
			counter_power++;
		}
		//Ending power calculation
		part_number = number2 % power;
		digit =  part_number / (power/10);
		digitSum = digitSum + digit;
		counter++;
	}

For example, 12345 = number, then part_number = 2345, then digit digit = 2345/1000 = 2 .
So on so forth until the loop reach digit=4.
When the loop is terminated, part_number = 45. Therefore, lastDigit=part_number/10 = 4. Then, it's trivial to calculate the sum of all digits.
At the end, there's an "if" to check whether the Sum is dividable by 9.

However, as I executed the .exe file. I kept receiving an pop-up that said : "Debug Error: Run-time check failure #3: variable part_number is being used without being initialized" .

As you saw, part_number has been definitely declared
I've been baffled by this without clues. Perhaps, I used many variables? 11 in this exercise.

Thanks so much for any hints!

my bad..it was a typo..I actually used &#37; 10 for the last digit in my source code.

I'm certain that I've been working with copy of input.
I'm not sure what caused the runtime-error though

to make my point clearer
I pasted my source code here

I atually got run-time error when inputing 2-digit number.
I suspected that the first while-loop is imperfect.

Code:

#include <iostream>
using namespace std;
int main()
{
	int number1,number2, firstDigit;
	int part_number, digit, lastDigit, digitTotalSum;
	int counter=1;
	int digitSum = 0;
	int digit_count=0;
	
	//Ask for number;
	cout << "Please enter a number: ";
	cin >> number1;
	//number2 will be used for later steps
	number2=number1;
	cout << endl;

	//First, we need to know how many digit it has
	//The loop keeps checking until number1 get to ZERO (false)
	//This loop will also calculate the power of base 10
	//in order to extract the 1st digit.
	int firstPower=1;
	while (number1)
	{
		number1 /= 10;
		firstPower *= 10;
		digit_count++;
	}
	//------------------------------------------------------

	
	//The first digit
	firstDigit=number2/(firstPower/10); 
	
	//This loop will take care of the middle digits
	while(counter < (digit_count - 1))
	{
		//Need to calcuate power of base 10
		int power=1;
		int counter_power=1;	
		while (counter_power<= (digit_count-counter))
		{
			power = power*10;
			counter_power++;
		}
		//Ending power calculation
		part_number = number2 &#37; power;
		digit =  part_number / (power/10);
		digitSum = digitSum + digit;
		counter++;
	}
	//------------------------------------------------------
	//This will calculate the last digit and the sum
	lastDigit=part_number % 10;
	digitTotalSum=digitSum + lastDigit+firstDigit;
	cout << "The sum is: " << digitTotalSum << endl;

uhmm i got your point!
how come I didn't think of that . I certainly will try it to shorten the code which I'm not really happy with.