what is wrong with the logic that i am using? - c++

Question

theres a logic error , for the code i m trying to do ,
*
**
***
**
*
so this is the pattern , what my code is running is this
*
**
***
**
**
**
there seems to be logic error for the printing of stars , i just wanted to know what logic should i use.
heres the code :-
#include<iostream>
using namespace std;
int main()
{
/*
*
**
***
**
*
*/
int i,rows;
cout<<"Enter number of rows :"<<endl;
cin>>rows;
for(i = 1; i <= ((rows/2)+1) ; i++)
{
for(int j = (rows - i); j >= 1; j--)
{
cout<<" ";
}
for(int k = 1; k <= i; k++)
{
cout<<"*";
}
cout<<endl;
}
for(i = ((rows/2)+1) ; i <= rows; i++)
{
for(int j = 1; j <= i; j++)
{
cout<<" ";
}
for(int k = (rows/2); k >= 1; k--)
{
cout<<"*";
}
cout<<endl;
}
return 0;
}

Answer 1

You can change your second loop as follows:
for ( i = ( rows / 2 ); i >= 1; i-- ) {
for ( int j = ( rows - i ); j >= 1; j-- ) {
cout << " ";
}
for ( int k = 1; k <= i; k++ ) {
cout << "*";
}
cout << endl;
}
It reuses the logic from the first loop, but just changes it to go from rows/2 down to 1 (inclusive) instead.
The first loop header also runs too many times for even values. For example, with 4, it does 4 / 2 + 1 which is 3. What you want is below.
for ( i = 1; i <= (int)( rows / 2. + .5 ); i++ )
This effectively rounds. So for 4 you now have 4 / 2. + .5 which is 2.5, then converted to int is 2. With 5, you get 5 / 2. + .5 which is 2.5 + .5 which is 3.0, then to an int is 3

Answer 2

You don't need to initialize i in the second for loop. Just let continue with the next row value after the first loop finishes.
The number of * you print is controlled by the k loop. In the first row loop you print out i of them, while in the second you always print out the same number - rows / 2. You'll want to print out a gradually reducing number of them - rows + 1 - i. Or just use for (int k = i; k <= rows; ++k).