Unable to understand pattern problem using loops

[Kartik24]

I was printing a pattern like this and found this code online.
AAAAA*
AAAA***
AAA*****
AA*******
A*********

When i calculated how the loop is working I found this that for first iteration the values of i,j and k are 1,5,1 respectively that means five "A" then *;for second loop I calculated the values 2,4,2 respectively.The second loop will run till j>=i which means 4,3,2 as i has been 2 now and j is 4 so there should be 3 "A" not four.Can you help me understand where my thought process is going wrong or how i am calculating their value wrong.

#include<iostream>
using std::endl;
using std::cout;

int main()
{
    for(int i=1;i<=5;i++)
    {

    for(int j=5;j>=i;j--)
      {
     cout<<"A";
      }

    for(int k=1;k<2*i;k++)
      {
      cout<<"*";
      }
     cout<<endl;
     }
}

Also is it useful to practice problems of this kind to get hang of loops or should i make generic programmes.

[wildblue]

I replaced the cout statements within the nested for loops with the current values of i and j, and i and k. I don't know if this will help visualize what's happening in the loop processing.

i 1 j 5
i 1 j 4
i 1 j 3
i 1 j 2
i 1 j 1
i 1 k 1

i 2 j 5
i 2 j 4
i 2 j 3
i 2 j 2
i 2 k 1
i 2 k 2
i 2 k 3

i 3 j 5
i 3 j 4
i 3 j 3
i 3 k 1
i 3 k 2
i 3 k 3
i 3 k 4
i 3 k 5

i 4 j 5
i 4 j 4
i 4 k 1
i 4 k 2
i 4 k 3
i 4 k 4
i 4 k 5
i 4 k 6
i 4 k 7

i 5 j 5
i 5 k 1
i 5 k 2
i 5 k 3
i 5 k 4
i 5 k 5
i 5 k 6
i 5 k 7
i 5 k 8
i 5 k 9

[Kartik24]

@wildblue sorry for the noob question but can u explain me why for the second loop the value for j start from 5 shouldn't it start from 4 as j--. Why isn't it value updated to 4.Also why does k start from 0 always.it would be really helpful if you can explain me or point me somewhere about how the variable updation is happening.

[wildblue]

For each time through the outside loop (i), the inside loops run fully from their initial value, that's 5 for j and 1 for k, through whatever number they end with in that particular run (which will depend on the current value of i).

i = 1 // start outside loop
  first nested loop   j=5 and decrements, 4, 3, 2, 1, 0; at 0 loop ends, condition j>=i no longer true 
  second nested loop  k=1 and increments, 2;             at 2 loop ends, condition k<2*i (2) no longer true
  new line
i = 2  // start outside loop again. Internal loops start back at their beginning state.
  first nested loop   j=5 and decrements, 4, 3, 2, 1;    at 1 loop ends, condition j>=i no longer true
  second nested loop  k=1 and increments, 2, 3, 4;       at 4 loop ends, condition k<2*i (4) no longer true
  new line
etc.

[dhayden]

why for the second loop the value for j start from 5 shouldn't it start from 4 as j--.

I think you don't fully understand how the for statement works. This:

for(int j=5;j>=i;j--) {
    doStuff;
}

is equivalent to:

{
    int j=5;
    while (j >= i) {
        doStuff;
        j--;
    }
}

Notice that the increment part (j--) happens at the end of the loop, not at the beginning.

[Kartik24]

Thanks for the help finally its clear to me where i was going wrong.