Swift Program to Display All Prime Numbers from 1 to N

This tutorial will discuss how to write a Swift program to display all prime numbers from 1 to N.

Prime numbers are those numbers that are greater than 1 and has exactly two factors that is 1 and the number itself. For example, 2 is the prime number because it has only two factors that are 1 and 2.

Below is a demonstration of the same ?

Suppose we enter the following input ?

Range - 1 to 20

Following is the desired output ?

Prime numbers between 1 to 20 are - 2, 3, 5, 7, 11, 13, 17, 19

Algorithm

Following is The algorithm to display all prime numbers from 1 to N ?

• Step 1 ? Create a function which will return the prime numbers named as "checkingPrimeNumber()".

• Step 2 ? Check if the given number is 1 or 0 using if statement. If the given number is 1 or 0 then return false. Which means the number is not prime number.

• Step 3 ? Run a for loop from 2 to num-1

• Step 4 ? Inside for loop check if the given number is divisible by j. If the number is divisible by j then return false, that means the number is not prime number otherwise the number is prime number so return true.

• Step 5 ? Create two variables that store lower and upper limit. Here the value of these variable can be pre-defined or user-defined.

• Step 6 ? Run another for loop from lower to upper limit.

• Step 7 ? Display all the prime numbers present in between the given range by calling the checkingPrimeNumber().

Example 1

The following program shows how to display all prime numbers from 1 to N.

<div class="execute"></div><div class="code-mirror  language-swift" 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> <span class="token class-name">Foundation</span>
<span class="token keyword">import</span> <span class="token class-name">Glibc</span>

<span class="token keyword">func</span> <span class="token function-definition function">checkingPrimeNumber</span><span class="token punctuation">(</span>num<span class="token punctuation">:</span> <span class="token class-name">Int</span><span class="token punctuation">)</span> <span class="token operator">-></span> <span class="token class-name">Bool</span><span class="token punctuation">{</span>
    
<span class="token comment">   // Checking if num for 1 or 0</span>
<span class="token comment">   // 1 and 0 are not prime number. </span>
<span class="token comment">   // So, if num is 1 or 0, then return false</span>
<span class="token comment">   // Which means the number is not prime number</span>
   <span class="token keyword">if</span><span class="token punctuation">(</span>num <span class="token operator">==</span> <span class="token number">1</span> <span class="token operator">||</span> num <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
      <span class="token keyword">return</span> <span class="token boolean">false</span>
   <span class="token punctuation">}</span>

<span class="token comment">   // For loop starts from 2 to num - 1</span>
   <span class="token keyword">for</span> j <span class="token keyword">in</span> <span class="token number">2</span><span class="token operator">..<</span>num<span class="token punctuation">{</span>

   <span class="token comment">// Checking the num is divisible by j, if yes </span>
   <span class="token comment">// then the num is not prime number</span>
      <span class="token keyword">if</span> <span class="token punctuation">(</span>num <span class="token operator">%</span> j <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
         <span class="token keyword">return</span> <span class="token boolean">false</span>
      <span class="token punctuation">}</span>
   <span class="token punctuation">}</span>
   <span class="token comment">// Else num is prime number</span>
   <span class="token keyword">return</span> <span class="token boolean">true</span>
<span class="token punctuation">}</span>
<span class="token keyword">var</span> lowerLimit <span class="token operator">=</span> <span class="token number">1</span>
<span class="token keyword">var</span> upperLimit <span class="token operator">=</span> <span class="token number">20</span>

<span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">"Range-</span><span class="token interpolation-punctuation punctuation">\(</span><span class="token interpolation">lowerLimit</span><span class="token interpolation-punctuation punctuation">)</span><span class="token string"> to </span><span class="token interpolation-punctuation punctuation">\(</span><span class="token interpolation">upperLimit</span><span class="token interpolation-punctuation punctuation">)</span><span class="token string">"</span></span><span class="token punctuation">)</span>
<span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">"Prime numbers are :"</span></span><span class="token punctuation">)</span>

<span class="token comment">// Checking for every number staring from</span>
<span class="token comment">// LowerLimit to upperLimit(that is 1 to 20)</span>
<span class="token keyword">for</span> k <span class="token keyword">in</span> lowerLimit<span class="token operator">...</span>upperLimit<span class="token punctuation">{</span>

   <span class="token comment">// Checking if the current number is  </span>
   <span class="token comment">// prime number or not</span>
   <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">checkingPrimeNumber</span><span class="token punctuation">(</span>num<span class="token punctuation">:</span> k<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">{</span>

      <span class="token comment">// Display only prime number</span>
      <span class="token function">print</span><span class="token punctuation">(</span>k<span class="token punctuation">)</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

<span class="typ">Range</span><span class="pun">-</span><span class="lit">1</span><span class="pln"> to </span><span class="lit">20</span><span class="pln">
</span><span class="typ">Prime</span><span class="pln"> numbers are </span><span class="pun">:</span><span class="pln">
</span><span class="lit">2</span><span class="pln">
</span><span class="lit">3</span><span class="pln">
</span><span class="lit">5</span><span class="pln">
</span><span class="lit">7</span><span class="pln">
</span><span class="lit">11</span><span class="pln">
</span><span class="lit">13</span><span class="pln">
</span><span class="lit">17</span><span class="pln">
</span><span class="lit">19</span>

Here, in the above code we create a function named as checkingPrimeNumber(), this function takes one argument and return the prime number. Now we declare two variables with values named as lowerLimit = 1 and upperLimit = 20. We iterate a for loop from 1 to 20 and display all the prime numbers present in between 1 to 20 by calling the checkingPrimeNumber() function.

Example 2

The following program shows how to display all prime numbers from 1 to N by taking user input.

<div class="code-mirror  language-swift" 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> <span class="token class-name">Foundation</span>
<span class="token keyword">import</span> <span class="token class-name">Glibc</span>

<span class="token keyword">func</span> <span class="token function-definition function">checkingPrimeNumber</span><span class="token punctuation">(</span>num<span class="token punctuation">:</span> <span class="token class-name">Int</span><span class="token punctuation">)</span> <span class="token operator">-></span> <span class="token class-name">Bool</span><span class="token punctuation">{</span>

<span class="token comment">   // Checking num for 1 or 0</span>
<span class="token comment">   // because 1 and 0 are not prime number. </span>
   <span class="token keyword">if</span><span class="token punctuation">(</span>num <span class="token operator">==</span> <span class="token number">1</span> <span class="token operator">||</span> num <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
      <span class="token keyword">return</span> <span class="token boolean">false</span>
   <span class="token punctuation">}</span>
   <span class="token comment">// For loop starts from 2 to num - 1</span>
   <span class="token keyword">for</span> j <span class="token keyword">in</span> <span class="token number">2</span><span class="token operator">..<</span>num<span class="token punctuation">{</span>
      <span class="token comment">// Checking the num is divisible by j, if yes </span>
      <span class="token comment">// then the num is not prime number</span>
      <span class="token keyword">if</span><span class="token punctuation">(</span>num <span class="token operator">%</span> j <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
         <span class="token keyword">return</span> <span class="token boolean">false</span>
      <span class="token punctuation">}</span>
   <span class="token punctuation">}</span>
   <span class="token comment">// Else the number is prime number</span>
   <span class="token keyword">return</span> <span class="token boolean">true</span>
<span class="token punctuation">}</span>
<span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">"Please enter lower range:"</span></span><span class="token punctuation">)</span>

<span class="token comment">// Enter the integer type lower range from the user</span>
<span class="token keyword">var</span> lowerLimit <span class="token operator">=</span> <span class="token class-name">Int</span><span class="token punctuation">(</span><span class="token function">readLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">!</span><span class="token punctuation">)</span><span class="token operator">!</span>
<span class="token function">print</span><span class="token punctuation">(</span>lowerLimit<span class="token punctuation">)</span>
<span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">"Please enter upper range:"</span></span><span class="token punctuation">)</span>

<span class="token comment">// Enter the integer type upper range from the user</span>
<span class="token keyword">var</span> upperLimit <span class="token operator">=</span> <span class="token class-name">Int</span><span class="token punctuation">(</span><span class="token function">readLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">!</span><span class="token punctuation">)</span><span class="token operator">!</span>
<span class="token function">print</span><span class="token punctuation">(</span>upperLimit<span class="token punctuation">)</span>
<span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">"Entered range is </span><span class="token interpolation-punctuation punctuation">\(</span><span class="token interpolation">lowerLimit</span><span class="token interpolation-punctuation punctuation">)</span><span class="token string"> to </span><span class="token interpolation-punctuation punctuation">\(</span><span class="token interpolation">upperLimit</span><span class="token interpolation-punctuation punctuation">)</span><span class="token string">"</span></span><span class="token punctuation">)</span>
<span class="token function">print</span><span class="token punctuation">(</span><span class="token string-literal"><span class="token string">"So following are the Prime numbers:"</span></span><span class="token punctuation">)</span>

<span class="token comment">// Checking for every number staring from</span>
<span class="token comment">// LowerLimit to upperLimit</span>
<span class="token keyword">for</span> k <span class="token keyword">in</span> lowerLimit<span class="token operator">...</span>upperLimit<span class="token punctuation">{</span>

<span class="token comment">   // Checking if the current number is  </span>
<span class="token comment">   // prime number or not</span>
<span class="token keyword">   if</span> <span class="token punctuation">(</span><span class="token function">checkingPrimeNumber</span><span class="token punctuation">(</span>num<span class="token punctuation">:</span> k<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">{</span>

      <span class="token comment">// Display only prime numbers</span>
      <span class="token function">print</span><span class="token punctuation">(</span>k<span class="token punctuation">)</span>
   <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</div>

STDIN Input

<span class="typ">Please</span><span class="pln"> enter lower range</span><span class="pun">:</span><span class="pln">
</span><span class="lit">1</span><span class="pln">
</span><span class="typ">Please</span><span class="pln"> enter upper range</span><span class="pun">:</span><span class="pln">
</span><span class="lit">30</span>

Output

<span class="typ">So</span><span class="pln"> following are the </span><span class="typ">Prime</span><span class="pln"> numbers</span><span class="pun">:</span><span class="pln">
</span><span class="lit">2</span><span class="pln">
</span><span class="lit">3</span><span class="pln">
</span><span class="lit">5</span><span class="pln">
</span><span class="lit">7</span><span class="pln">
</span><span class="lit">11</span><span class="pln">
</span><span class="lit">13</span><span class="pln">
</span><span class="lit">17</span><span class="pln">
</span><span class="lit">19</span><span class="pln">
</span><span class="lit">23</span><span class="pln">
</span><span class="lit">29</span>

Here, in the above code we take the value of lower limit and upper limit from the user and display all the prime numbers in between the specified range by calling checkingPrimeNumber() function.