How to better understand nested loops? - c++

Question

My problem is that I don't understand nested loops well enough to answer this problem. I'm supposed to right-align a stack that I've made on a left alignment using nested for loops, but I can't quite figure out the conditions on the two inner ones.
Correct answer:
Height = 8
.......#
......##
.....###
....####
...#####
..######
.#######
########
My answer:
Height = 8
.......#
.......#......#
.......#......#.....#
.......#......#.....#....#
.......#......#.....#....#...#
.......#......#.....#....#...#..#
.......#......#.....#....#...#..#.#
.......#......#.....#....#...#..#.##
I've played around with it, took it seriously and nothing. I did (k = 7, k > j, k--), (k = 0, k < n-1, k++), k < j+7, I drew tables and i know that the height is pretty much the same as the value of the spaces but inverted on each line. I also know that the value of the hashes and the spaces should be equal to the height input by user.
It's supposed to take in a value from user, but I've worked on it on a separate file with the value n being the height to simplify and work on it without the rest of the program.
#include <stdio.h>
int main(void) {
int n = 8;
for (int i = 0; i < n; i++) {
for (int j = 0; j < i; j++) {
for(int k = 7; k > j; k--) {
printf(".");
}
printf("#");
}
printf("\n");
}
}

Answer 1

It's actually pretty simple. Write a table with each line and how many spaces and '#' you need to print:
n == 8
| output | line | num_spaces | num_signs |
| -------- | ---- | ---------- | --------- |
| .......# | 1 | 7 | 1 |
| ......## | 2 | 6 | 2 |
| .....### | 3 | 5 | 3 |
| ....#### | 4 | 4 | 4 |
| ...##### | 5 | 3 | 5 |
| ..###### | 6 | 2 | 6 |
| .####### | 7 | 1 | 7 |
| ######## | 8 | 0 | 8 |
For line you can start from 0 or from 1 or from n and go backwards. Pick something that is the easiest. You will see that starting from 1 is the simplest in your example.
Now for each line we need to determine how many num_spaces and num_signs we print. They should depend on line and on n.
For num_spaces it's n - line and for num_signs it's line
So the code should look like this:
// for each line
for (int line = 1; line <= n; ++line)
{
// print n - line spaces
// print line # characters
// print \n
}
With loops the code will look like this:
// for each line
for (int line = 1; line <= n; ++line)
{
// print n - line spaces
for (int i = 0; i < n -line; ++i)
std::cout << ' ';
// print line # characters
for (int i = 0; i < line; ++i)
std::cout << '#';
std::cout << '\n';
}
std::cout.flush();
But that's actually not recommended. You can get rid of those inner loops. One good and easy way is to use strings:
// for each line
for (int line = 1; line <= n; ++line)
{
// print n - line spaces
std::cout << std::string(n - line, ' ');
// print line # characters
std::cout << std::string(line, '#');
std::cout << '\n';
}
std::cout.flush();
And you can go even one step further:
// for each line
for (int line = 1; line <= n; ++line)
{
// print n - line spaces and line # characters
std::cout << std::string(n - line, ' ') << std::string(line, '#') << '\n';
}
std::cout.flush();