How to print sideways pyramid without using conditional statement?

Question

I have to print out a sideways pyramid:

O

OO

OOO

OOOO

OOO

OO

O

I have managed to do it using two for loops and an if statement but I want to know if it possible to do it using two for loops and no conditional statements.

char character = 79;
int temp = 1;

for (int i = 0; i < 7; i++)
{
    std::cout << character;
    
    if (i >= 4) 
    {
        temp = temp + 2;
    }

    for (int j = 0 + temp; j <= i; j++)
    {
        std::cout << character;
    }

    std::endl(std::cout);
}

@Chris I'm using temp just bc I couldn't think of any other way — me22x, Oct 08 '21 at 20:36
`char character = 79;` Refrain from [magic numbers](https://stackoverflow.com/questions/47882/what-is-a-magic-number-and-why-is-it-bad). Use `char character = 'O';` instead. — user4581301, Oct 08 '21 at 20:39
Yes, it is possible to do it with two loops an no conditional statements. Consider `for (int i = 0; i < 4; i++)` as your first loop and `for ( ; i < 7; i++)` as your second. — Drew Dormann, Oct 08 '21 at 20:44

Chris · Answer 1 · 2021-10-08T21:05:37.577

It's possible to do with two (or 1, with a helper function) loops, nested. Oh, and some math.

Consider that we can write a function really easily to print a row.

void print_row(char ch, int len) {
    for (int i = 0; i < len; i++) {
        std::cout << ch;
    }

    std::cout << std::endl;
}

If we call that we only need 1 loop. If we loop to a certain size, we really need to go to size times 2 minus 1. What number is generated each time?

const int size = 4;

for (int i = 1; i <= size * 2 - 1; i++) {
    ...
}

What we really need are these numbers, though, to give to print_row:

Up until we get to 5, it's all good. For 5 and above, we need to get back to lower numbers. We can use a ternary operator and some math to get there.

const int size = 4;

for (int i = 1; i <= size * 2 - 1; i++) {
    int len_of_row = (i <= size ? i : size - (i - size));
    print_row('0', len_of_row);
}

Let's pick that apart. i - size when i is 5 and size is 4 will give us 1. If we subtract that from our size, we get 3. If we do the same with i being 6, we get 2, and if we do it with 7 we get 1.

Now, maybe the ternary is a cheat because it's a replacement for a conditional.

We can eliminate the ternary expression by taking advantage of operator precendence and how boolean logic short-circuits. We do have to rewrite print_row turn return bool and always return true.

const int size = 4;

for (int i = 1; i <= size * 2 - 1; i++) {
    i <= size && print_row('0', i) || print_row('0', size - (i - size);
}

How to print sideways pyramid without using conditional statement?

1 Answers1