在c ++中的for循环中，如何使用

Question

What I'm dealing with is a nested for loop that finds perfect numbers. The iterations to find the perfect number came about pretty quickly. However, I need the output to show a string that says, "perfect number found" and have that happen once. Then on the same line, print out all the perfect numbers. So for example, lets say I have two inputs, 1 to 30.

That means that the perfect numbers are 6 and 28. The output should be something like.

Perfect numbers: 6 28.

What I'm confused on is how to print out just that string once in the for loop I have created. Here's what I have so far.

#include <iostream>

int main()
{
    int a, b;
    std::cin >> a >> b;
    int count = 0;

    for (int i = a; i <= b; i++)
    {
        int sum = 0;
        for (int j = 1; j <= i; j++)
        {
            if (i % j == 0)
            {
                sum += j;
            }
        }
        if (i * 2 == sum)
        {
            std::cout << i << " ";
            count++;
        }
    }
    std::cout << "\n";
    std::cout << "number of perfect numbers found: " << count << std::endl;

    return 0;
}

Answer 1

Why do it "in the for loop"? Do it before you enter the for loop.

Or, if you want to make sure you found at least one perfect number before committing yourself to printing that string, then on the line where you print out the individual values, instead of:

std::cout << i << " ";

just say:

std::cout << (count == 0 ? "Perfect numbers: " : "") << i << " ";

Answer 2

you can try something like this and just add the print with the cout

for(i=start; i<=end; i++)
    {
        sum = 0;

        /* Check whether the current number i is Perfect number or not */
        for(j=1; j<i; j++)
        {
            if(i % j == 0)
            {
                sum += j;
            }
        }

        /* If the current number i is Perfect number */
        if(sum == i)
        {
            cout <<i<<" ,";
        }
    }