can anyone explain me this full code...to print this pattern

Question

#include <iostream>
using namespace std;

int main() {
int b; int length=5; int j;
for (int i=0;i<=length;++i) //here length = 5
{
int b=9;
for (j=0;j<length-i;j++) //for blank spaces
cout<<" ";
for(j=0;j<2*i+1;j++)
{
if(j<(2*i+1)/2) cout<<b--;
else cout<<b++;
}
cout<<"\n";

}
return 0;
}

Answer 1

There is a few places where things could be improved. This code basically prints numbers in a few nested for loops.

commented code for you:

\\includes for input and output streams
#include <iostream>
\\using standard namespace
using namespace std;

\\main entry point
int main() {
\\declare 3 variables, assign 5 to length
int b; int length=5; int j;
\\ make a for loop starting at 0
\\ loop until it is less than or equal to length
\\ length is 5 so it will run 0,1,2,3,4,5 (6 times)
\\ it will increase by 1 each time until then
for (int i=0;i<=length;++i)
{

\\this code here will run 6 times as explained
\\it sets b to 9 every time
int b=9;

\\another for loop notice there is no braces so
\\it only executes next line
for (j=0;j<length-i;j++)
\\that line just prints spaces (6 of them)
cout<<" ";
\\another for loop from 0 to (2 times i)
\\ i is the variable that is being looped from earlier
\\ so j loops from 0 to (0, 2, 4, 6, 8,10)
for(j=0;j<2*i+1;j++)
{
\\if j <= i (this could be written much better)
\\ then print b then take 1 from it (starts as 9)
if(j<(2*i+1)/2) cout<<b--;
\\otherwise print b then add 1 to it
else cout<<b++;
}
\\finally start a new line
cout<<"\n";

}
\\exit the main entry point and return 0
return 0;
}