Swift Program to Print Downward Triangle Star Pattern

This tutorial will discuss how to write swift program to print downward triangle star pattern.

Star pattern is a sequence of “*” which is used to develop different patterns or shapes like pyramid, rectangle, cross, etc. These star patterns are generally used to understand or practice the program flow controls, also they are good for logical thinking.

To create a downward triangle star pattern we can use any of the following methods −

  • Using nested for loop

  • Using init() Function

  • Using stride Function

Below is a demonstration of the same −

Input

Suppose our given input is −

Num = 5

Output

The desired output would be −

 *******
  ******
   *****
    ****
     ***
      **
       *

Method 1 - Using Nested For Loop

We can create a downward triangle star pattern or any other pattern using nested for loops. Here each for loop handle different tasks such as outermost for loop is used for new rows, 1st nested for loop is used for white spaces, and 2nd nested for loop is used for “*”.

Example

The following program shows how to print downward triangle star pattern using nested for loop.

import Foundation
import Glibc

// Height of the downward triangle star pattern
let num = 8

// Outer for loop is used to handle the total
// number of rows in downward triangle star pattern
for i in 1..<num{

   // Nested for loop is used to print white
   // spaces
   for _ in 1...i{
      print(terminator: " ")
   }
   
   // Nested for loop is used to print
   // downward triangle star pattern
   for _ in 1...num-i{
      print("*", terminator: "")
   }
   
   // Add new line
   print("")
}

Output

 *******
  ******
   *****
    ****
     ***
      **
       *

Here, in the above code, we uses nested for loops to print downward triangle star pattern. The outer most for loop(starts from 1 to 7) is use to handle the total number of rows are going to print and each row is start with new line. Now the first nested for loop(starts form 0 to i) is used to print the white spaces and in each iteration the white space is increase by one. And the second nested for loop is used to print downward triangle using “*”.

Method 2 - Using init() Function

Swift provide an in-built function named String.init(). Using this function we can able to create any pattern. String.init() function create a string in which the given character is repeated the specified number of times.

Syntax

Following is the syntax −

String.init(repeating:Character, count: Int)

Here, repeating represent the character which this method repeats and count represent the total number of time the given character repeat in the resultant string.

Example

The following program shows how to print downward triangle star pattern using string.init() function.

import Foundation
import Glibc

// Height of the downward triangle star pattern
var num = 4
var x = num

// Creating downward triangle star pattern
// Using String.init() function
while x >= 1{
   print(String.init(repeating: " ", count: num-x) + String.init(repeating: "*", count: x))
   x -= 1
}

Output

****
 ***
  **
   *

Here in the above code, we create a downward triangle star pattern of height 4 using String.init() function. Here we use while loop(x >= 1) which starts from 4 and in each iteration the value of x is decrease by one. So String.init(repeating: " ", count: num-x) is used to print spaces, here in every iteration the init() function repeats the white spaces according to the count value(that is num-x) and in every iteration the white space is increased by one. And String.init(repeating: "*", count:x) is used to print “*” in downward triangle star pattern, here in each iteration init() function repeats “*” according to the value of count(that is x). So the working of the above code is −

num = 4

In 1st iteration −

print(String.init(repeating: " ", count: 4-4) + String.init(repeating: "*", count: 4))

So it print 0 space and 4 “*”

In 2nd iteration x = 3 −

print(String.init(repeating: " ", count: 4-3) + String.init(repeating: "*", count: 3)

So it print 1 space and 3 “*”

…. so on till 4th iteration and print downward triangle star pattern.

Method 3 - Using stride Function

Swift provide an in-built function named stride(). The stride() function is used to move from one value to another with increment or decrement. Or we can say stride() function return a sequence from the starting value but not include end value and each value in the given sequence is steps by the given amount.

Syntax

Following is the syntax −

stride(from:startValue, to: endValue, by:count)

Here,

from − Represent the starting value to used for the given sequence.

to − Represent the end value to limit the given sequence

by − Represent the amount to step by with each iteration, here positive value represent upward iteration or increment and negative value represent the downward iteration or decrement.

Example

The following program shows how to print downward triangle star pattern using stride() function.

import Foundation
import Glibc

// Height of the downward triangle star pattern
let num = 9
for i in 1..<num{

   // Printing white spaces
   for _ in 1...i{
      print(terminator : " ")
   }
   
   // Printing downward triangle star pattern
   for _ in stride(from: i, to: num, by: 1){
      print("*", terminator : "")
   }
   
   // New line after each row
   print(" ")
}

Output

 ******** 
  ******* 
   ****** 
    ***** 
     **** 
      *** 
       ** 
        *

Here in the above code, we use three nested for loops. The outermost for loop (starts from 1 to 8) is used to handle the total number of rows are going to print and each row starts with a new line. The first nested for-loop is used to print white spaces and in each iteration the white space is increased by one.

for _ in 1...i { 
   print(terminator : " ") 
}

The second nested for loop is used to print “*” in downward triangle pattern. Here stride() function is used to print ”*”. In this function, the iteration started from i to num and in each iteration the value is increase by one.

for _ in stride(from: i, to: num, by: 1) {   
   print("*", terminator : "") 
}

Updated on: 03-Nov-2022

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