Print a diamond given a user-specified odd number

gistfile1.txt

// Diamond Printer
// Prompt the user for the max number of asterisks, must be Odd
// Then print a symmetrical diamond, centered.
// Jesse Rhoads jesserhoads@gmail.com

package main

import (
	"fmt"
	"strings"
)

var maxNumAsterisks int

// centers a string (s) to fit within given width (w)
func center(s string, w int) string {
	return fmt.Sprintf("%[1]*s", -w, fmt.Sprintf("%[1]*s", (w + len(s))/2, s))
}

// Print a specific number of asterisks, centered.
// Assumes global variable maxNumAsterisks is set.
func asteriskPrint(asterisks int, maxNumAsterisks int) {
	numAsterisks := strings.Repeat(string('*'), asterisks)
	fmt.Println(center(numAsterisks, maxNumAsterisks))
	return
}

func main() {
	fmt.Println("Diamond Printer")
	for {
		fmt.Print("Please Enter an Odd number: ")
		var n int
		fmt.Scanln(&n)
		if( n % 2 == 0 ) {
			fmt.Println(n,"is an Even number, please try again!")
		} else {
			maxNumAsterisks = n
			break
		}
	}

	// We are going to print a asterisk of *'s. assumption is that we will have a
	// maxNumasterisks which is ideally an odd number
	// count up to the max and then back down again, centering the string.
	for i := 0; i < maxNumAsterisks; i += 1 {
		if i % 2 != 0 {
			asteriskPrint(i, maxNumAsterisks)
		}
	}
	// Now we do the same, counting back down.  Reverse for loops and
	// decrementing by 2 does not seem to work safely!
  	da := maxNumAsterisks
	for {
		// If it is an odd number, print it.
		if da % 2 != 0 {
			asteriskPrint(da, maxNumAsterisks)
		}
		da--
		if da < 1 {
			break
		}
	}
}