BubbleSort implemented with do-while loop

I am learning basic sorting algorithms. I wrote below but no sure why it never completely sorts it? I thought it would only meet the exit criteria (flag not set to 1) if it iterates over the entire array with no sorting needed.

void bubbleSort(int lst[], int size)
{
    int flag; 
    do{
    for(int i = 0; i < size-1; i++) 
    {
        flag = 0; //nothing sorted yet 
        int temp = lst[i];
        if(lst[i] > lst[i + 1])
        {
            //swap values  
            int temp = lst[i]; 
            lst[i] = lst[i + 1];
            lst[i+1] = temp; 
            flag = 1; //sort happened set flag 
        }

    }
    }while (flag != 0); 
}

You were almost there. All you need to do is move where you initialize the flag:

void bubbleSort(int lst[], int size) {
    int flag;
    do {
        flag = 0; //nothing sorted yet
        for(int i = 0; i < size-1; i++) {
            int temp = lst[i];
            if(lst[i] > lst[i + 1]) {
                //swap values
                int temp = lst[i];
                lst[i] = lst[i + 1];
                lst[i+1] = temp;
                flag = 1; //sort happened set flag
            }
        }
    } while (flag != 0);
}

If you set flag to 0 within the for loop, then any time you set flag within the if, the flag will get reset on the next iteration of the for loop.

Like the answer fro David, but now in a more C++ style with some coding advices. Like checking your input, using std::span, std::vector, std::swap and in the output a range based for loop

#include <iostream>
#include <span>
#include <vector>

// never use : using namespace std;

void bubbleSort(std::span<int> values)
{
	//int flag; Use a better name and a boolean type
	// it will make your code more readable
	bool something_got_sorted{ false };

	// never trust your input so validate if sorting can happen
	// your original code would be invalid for an array of size 0 or 1
	if (values.size() < 2) return;

	do
	{
		something_got_sorted = false;

		for (std::size_t i = 0; i < values.size() - 1ul; ++i)
		{
			if (values[i] > values[i + 1ul])
			{
				// C++ has a swap function so use it makes the code more readable too
				// anytime you have to write a comment remove it and make
				// or use a function with a readable name (based on what you would have typed in the comment)
				std::swap(values[i], values[i + 1]);
				something_got_sorted = true;
			}
		}
	} while (something_got_sorted);
}

int main()
{
	// input array (note note a "C" style array)
	std::vector<int> values{ 9,3,5,6,4,2,1,0,8,7 };

	// note size does not have to be passed seperately
	bubbleSort(values);

	for (const auto value : values)
	{
		std::cout << value << " ";
	}

	return 0;
}

The problem itself is in its flag, which is being initialized at each iteration of the for loop.
To fix just move the declaration and initialization of the flag variable out of the do while loop.

void bubbleSort(int lst[], int size) {
    int flag = 0; // Initialize for do loop
    do {
        flag = 0; // Nothing sorted yet
        for (int i = 0; i < size - 1; i++) {
            int temp = lst[i];
            if (lst[i] > lst[i + 1]) {
                // swap values
                lst[i] = lst[i + 1];
                lst[i + 1] = temp;
                flag = 1; // Sort happened, set flag
            }
        }
    } while (flag != 0);
}