# Lecture notes on iteration

2007 July 11

For my CE 21 class. The problem discussed earlier was, draw a triangle of stars given the length for a side of the triangle n. It can be illustrated as follows for n = 3.

` * *`

The next task is to center the triangle:

Then we want to be able to print a diamond

` * `

This C++ code is one of the solutions to the problem:

`#include int main() { int n; std::cin >> n; int i = 1; // upper triangle while( i <= n ) { int space = n - i; for(int j = 1 ; j <= space ; j++ ) { std::cout << " “; } int j = 1; while( j <= i ) { std::cout <<”* “; j++; } std::cout << std::endl; i++; } // lower triangle i = n - 1; while( i >= 1 ) { int space = n - i; for(int j = 1 ; j <= space ; j++ ) { std::cout <<” “; } int j = 1; while( j <= i ) { std::cout <<”* “; j++; } std::cout << std::endl; i–; } return 0;}`

For the homework, answer the Challenge section of the lecture slides on iterations:

• Draw a pine tree with 3 sections

• Each section should have n lines of stars

• The start of the next section should have one less star than the end of the previous section

• Add n lines of single asterisks for a stand

Example for n = 3:

``````<code>      *
* *
* * *
* *
* * *
* * * *
* * *
* * * *
* * * * *
*
*
*</code>``````

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