For Loop

[Kevin S]

Thank you for your time and explanation here guys. I don't understand how it outputs K from 1 to 12 then 123 in this code...

#include <cstdlib>
#include <iostream>
#include <string>
#include <iomanip>
#include <cmath>

using namespace std;

int main()
{
	int i, j, k;

	for(i = 1; i <= 7; i++)
	{
		for (k = 1; k <= i; k++) cout << k; for (j = 7 - i; j >= 1; j--) cout << "*"; cout << "\n";
	}

		
	system("PAUSE");
	return EXIT_SUCCESS;
}

[shadder]

Hi,

This is a nested loop, k goes from 1 to i, as you can see in line 13 i goes from 1 to 7. Each time i iterates the loop inside (line 14) is executed and k goes from 1 to i's value at that particular loop.

Drawing a flow-chart may help you visualize

hope it helps

[Kevin S]

Thank you so much, what I am confused is that it is k++, right, k from 1 to 2, from 2 to 3, how can it be from 1 to 12? that's k+11...., then 12 to 123?

[48T7M4Gy]

#include <iostream>

int main()
{
    
    for(int i = 1; i <= 7; i++)
    {
        std::cout << "i = " << i << " k = ";
        
        for (int k = 1; k <= i; k++)
        {
            std::cout << k << '-';
        }
        std::cout << " j = ";
        
        for (int j = 7 - i; j >= 1; j--)
        {
            std::cout << j << '-';
        }
        
        std::cout << '\n';
    }
    return 0;
}

i = 1 k = 1- j = 6-5-4-3-2-1-
i = 2 k = 1-2- j = 5-4-3-2-1-
i = 3 k = 1-2-3- j = 4-3-2-1-
i = 4 k = 1-2-3-4- j = 3-2-1-
i = 5 k = 1-2-3-4-5- j = 2-1-
i = 6 k = 1-2-3-4-5-6- j = 1-
i = 7 k = 1-2-3-4-5-6-7- j = 
Program ended with exit code: 0

[Kevin S]

THANK YOU!!! KEMORT!!

My question is:

In the first for loop (i), the number goes on from 1 to 2, i=1 changed to i=2, just one action.

for(int i = 1; i <= 2; i++), why doesn't this loop output i=1, then i=12...

but for the second for loop (k), why the previous existing old number are kept (two actions), instead of going from 1 to 2, it goes from 1, to 1-2-, what happens in the (k) loop when (i ) goes from 1 to 2?

for (int k = 1; k <= 2; k++) { cout <<k<<'-';}

Excuse me if I am too slow lol

[48T7M4Gy]

@Kevin S
The best way to explain this is for you to use a pencil and paper and follow the recipe line by line.

If you compare the layout of the program in my version to that in the original you can see straight away mine is clearer. Also by putting in the additional separator characters what appear to be the number 12 is actually two separate numbers 1 and then 2. Both of these are tricks used to deliberately obscure a very simple nested loop arrangement.

[Kevin S]

Thanks again Kemort.

I can fully understand the combination of 1 and 2 to make them appearing like 12.

The place where I don't understand is why in the k loop (second loop), it keeps adding up, 1, then 1+2, but the first loop jumps from 1 to 2 (without 1 this time).

[48T7M4Gy]

The reason is that when the program hits line 10 the for loop there starts and runs until it completes.

The program then, having completed that loop, starts running at line 14, then 16 at which point that loop proceeds to completion ...

[Kevin S]

Thank you Kemort!