Swift program to Print Reverse Pyramid Star Pattern

This tutorial will discuss how to write swift program to print reverse pyramid 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 reverse pyramid 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 reverse pyramid of "*" 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 reverse pyramid star pattern using nested for loop.

<div class="execute"></div><div class="code-mirror  language-javascript" contenteditable="plaintext-only" spellcheck="false" style="outline: none; overflow-wrap: break-word; overflow-y: auto; white-space: pre-wrap;"><span class="token keyword">import</span> Foundation
<span class="token keyword">import</span> Glibc
<span class="token comment">// Height of the reverse pyramid</span>
<span class="token keyword">let</span> num <span class="token operator">=</span> <span class="token number">7</span>
<span class="token comment">// Outer for loop is used to handle the</span>
<span class="token comment">// total number of rows in reverse pyramid</span>
<span class="token keyword">for</span> i <span class="token keyword">in</span> <span class="token number">1.</span><span class="token punctuation">.</span><span class="token operator"><</span>num<span class="token punctuation">{</span>
   <span class="token comment">// Nested for loop is used to print white</span>
   <span class="token comment">// spaces</span>
   <span class="token keyword">for</span> _ <span class="token keyword">in</span> <span class="token number">1.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>i<span class="token punctuation">{</span>
      <span class="token function">print</span><span class="token punctuation">(</span>terminator<span class="token operator">:</span> <span class="token string">" "</span><span class="token punctuation">)</span>
   <span class="token punctuation">}</span>
   <span class="token comment">// Nested for loop is used to print reverse pyramid of "*"</span>
   <span class="token keyword">for</span> _ <span class="token keyword">in</span> <span class="token number">1.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>num<span class="token operator">-</span>i<span class="token punctuation">{</span>
      <span class="token function">print</span><span class="token punctuation">(</span><span class="token string">"*"</span><span class="token punctuation">,</span> terminator<span class="token operator">:</span> <span class="token string">" "</span><span class="token punctuation">)</span>
   <span class="token punctuation">}</span>
   <span class="token comment">// Add new line</span>
   <span class="token function">print</span><span class="token punctuation">(</span><span class="token string">""</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</div><div class="output-wrapper"><div class="console-close"></div><div class="code-output"></div></div>

Output

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

Here, in the above code, we uses nested for loops to print reverse pyramid of "*". The outer most for loop(starts from 1 to 6) 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 "*". As we can see from the output the "*" are the print in odd number, so this loop starts from 1 to num-i to print the desired result.

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 reverse pyramid star pattern using string.init() function.

<div class="execute"></div><div class="code-mirror  language-javascript" contenteditable="plaintext-only" spellcheck="false" style="outline: none; overflow-wrap: break-word; overflow-y: auto; white-space: pre-wrap;"><span class="token keyword">import</span> Foundation
<span class="token keyword">import</span> Glibc

<span class="token comment">// Height of the reverse pyramid</span>
<span class="token keyword">var</span> num <span class="token operator">=</span> <span class="token number">8</span>
<span class="token keyword">var</span> x <span class="token operator">=</span> num

<span class="token comment">// Creating reverse pyramid star pattern</span>
<span class="token comment">// Using String.init() function</span>
<span class="token keyword">while</span> x <span class="token operator">>=</span> <span class="token number">1</span><span class="token punctuation">{</span>
   <span class="token function">print</span><span class="token punctuation">(</span>String<span class="token punctuation">.</span><span class="token function">init</span><span class="token punctuation">(</span>repeating<span class="token operator">:</span> <span class="token string">" "</span><span class="token punctuation">,</span> count<span class="token operator">:</span> num<span class="token operator">-</span>x<span class="token punctuation">)</span> <span class="token operator">+</span> String<span class="token punctuation">.</span><span class="token function">init</span><span class="token punctuation">(</span>repeating<span class="token operator">:</span> <span class="token string">"*"</span><span class="token punctuation">,</span> count<span class="token operator">:</span> <span class="token punctuation">(</span><span class="token number">2</span><span class="token operator">*</span>x<span class="token punctuation">)</span> <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
   x <span class="token operator">-=</span> <span class="token number">1</span>
<span class="token punctuation">}</span>
</div><div class="output-wrapper"><div class="console-close"></div><div class="code-output"></div></div>

Output

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

Here in the above code, we create a reverse pyramid of height 8 using String.init() function. Here we use while loop (x >= 1) which starts from 8 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 value of count is increased by one. And String.init(repeating: "*", count: (2*x) - 1) is used to print "*" in reverse pyramid pattern, here in each iteration init() function repeats "*" according to the value of count(that is (2*x) - 1). So the working of the above code is ?

num = 8

In 1st iteration x = 8 ?

print(String.init(repeating: " ", count: 8-8) + String.init(repeating: "*", count: (2*8) - 1))

So it print 0 spaces and 15 "*"

In 2nd iteration x = 7 ?

print(String.init(repeating: " ", count: 8-7) + String.init(repeating: "*", count: (2*7) - 1))

So it print 6 spaces and 13 "*"

?.so on till 8th iteration and print reverse pyramid.

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 use 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 represents upward iteration or increment and negative value represent the downward iteration or decrement.

Example

The following program shows how to print reverse pyramid star pattern using stride() function.

<div class="execute"></div><div class="code-mirror  language-javascript" contenteditable="plaintext-only" spellcheck="false" style="outline: none; overflow-wrap: break-word; overflow-y: auto; white-space: pre-wrap;"><span class="token keyword">import</span> Foundation
<span class="token keyword">import</span> Glibc

<span class="token comment">// Height of the reverse pyramid</span>
<span class="token keyword">let</span> num <span class="token operator">=</span> <span class="token number">9</span>
<span class="token keyword">for</span> i <span class="token keyword">in</span> <span class="token number">1.</span><span class="token punctuation">.</span><span class="token operator"><</span>num<span class="token punctuation">{</span>
   
   <span class="token comment">// Printing white spaces</span>
   <span class="token keyword">for</span> _ <span class="token keyword">in</span> <span class="token number">1.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>i<span class="token punctuation">{</span>
      <span class="token function">print</span><span class="token punctuation">(</span>terminator <span class="token operator">:</span> <span class="token string">" "</span><span class="token punctuation">)</span>
   <span class="token punctuation">}</span>
   
   <span class="token comment">// Printing reverse pyramid of "*"</span>
   <span class="token keyword">for</span> _ <span class="token keyword">in</span> <span class="token function">stride</span><span class="token punctuation">(</span><span class="token parameter">from<span class="token operator">:</span> i<span class="token punctuation">,</span> to<span class="token operator">:</span> num<span class="token punctuation">,</span> by<span class="token operator">:</span> <span class="token number">1</span></span><span class="token punctuation">)</span><span class="token punctuation">{</span>
      <span class="token function">print</span><span class="token punctuation">(</span><span class="token string">"*"</span><span class="token punctuation">,</span> terminator <span class="token operator">:</span> <span class="token string">" "</span><span class="token punctuation">)</span>
   <span class="token punctuation">}</span>
   
   <span class="token comment">// New line after each row</span>
   <span class="token function">print</span><span class="token punctuation">(</span><span class="token string">" "</span><span class="token punctuation">)</span>
<span class="token punctuation">}</span>
</div><div class="output-wrapper"><div class="console-close"></div><div class="code-output"></div></div>

Output

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

Here in the above code, we uses 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 pyramid 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 : " ") 
}