Simplification of For Loop with different inputs

I would like to know if anyone of you has an idea of how I could choose the values in order to not to have the for loop repeated for every input. Thank you in advance.

#include <iostream>
using namespace std;

int main()
{
  
        int a, b, c, d, e, f, g, h, i;

    std::cout << "Please enter a number from 1 to 8: ";
    std::cin >> i;
    std::cout << "The value you entered is " << i; 
    std::cout << "\n";

    if (0 <= i <= 8) {
        if (i == 8) {
            for (a = 1; a <= 8; a++)
            {
                std::cout << "\n";

                for (c = 7; c >= a; c--) {
                    std::cout << " ";
                }

                for (b = 1; b <= a; b++) {

                    std::cout << "#";
                }


            }
        }
        else if (i == 7) {
            for (a = 2; a <= 8; a++)
            {
                std::cout << "\n";
                
                for (c = 7; c >= a; c--) {
                    std::cout << " ";
                }
                for (b = 1; b <= a; b++) {

                    std::cout << "#";
                }
            }
        }
        else if (i == 2) {
            for (a = 7; a <= 8; a++)
            {
                std::cout << "\n";

                for (c = 7; c >= a; c--) {
                    std::cout << " ";
                }
                for (b = 1; b <= a; b++) {

                    std::cout << "#";
                }
            }
        }
    }

  
    return 0;
}

Here I would like to put all the loops together, meaning I dont have to type in the same loop for every integer

>Solution :

First, let me point out that this does not mean what you think it does:

if (0 <= i <= 8)

In C++, you need to write it like this:

if (0 <= i && i <= 8)

Now on to your loops. You wrote out three loops, for the cases where i is 8, 7, and 2, but I assume you also wants loops for the other acceptable values of i.

The only differences between your loops are what i must be and what a starts at:

What is the relationship between i and the initial a here? I notice that i + a == 9 in all three cases. So we can compute a = 9 - i.

if (0 <= i && i <= 8) {
    for (a = 9 - i; a <= 8; a++) {
        std::cout << "\n";
    
        for (c = 7; c >= a; c--) {
            std::cout << " ";
        }
    
        for (b = 1; b <= a; b++) {
            std::cout << "#";
        }
    }
}