Swift Program to Find Sum of Even Fibonacci Terms Till number N

This tutorial will discuss how to write a Swift program to find sum of even fibonacci terms till number N.

A series of numbers in which every number is the sum of the two preceding numbers is known as Fibonacci series. The starting number of the Fibonacci series is 0 and 1, so the series is ?

0, 1, 1, 2, 3, 5, 8, 13, 21, ??

A number that is multiple of two is known as the even number. Or in other words, a number that is completely divisible by two is known as even number. For example, 2, 4, 6, 8, etc.

So we find the sum of even fibonacci terms till number N.

Below is a demonstration of the same -

Input

Suppose our given input is

Enter the number - 10

Output

The desired output would be ?

Sum of even Fibonacci terms are 10

Here the output is 10 because the even numbers present from 0 to 10 in fibonacci series are 2 and 8 so 2+8 = 10.

Algorithm

Following is the algorithm ?

• Step 1 ? Create a function.

• Step 2 ? Declare four variables with values name as "temp", "sum", "n1", "n2". Here sum is used to store the sum of even terms, n1 and n2 are the initial two value of fibonacci series.

• Step 3 ? Run a while loop till n2 <num.

• Step 4 ? use if statement to check for even numbers and find their sum.

if (n2 % 2 == 0) { 
   sum += n2 
}

• Step 5 ? Adding two previous numbers to find ith number of the series.

• Step 6 ? Return the sum of even numbers.

• Step 7 ? Call the function with argument and print output.

Example 1

The following program shows how to find the sum of even fibonacci terms till number N.

<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">// Function to find the sum of even fibonacci terms</span>
func <span class="token function">SumOfEvenFibonacci</span><span class="token punctuation">(</span>num<span class="token operator">:</span> Int<span class="token punctuation">)</span> <span class="token operator">-</span><span class="token operator">></span> Int<span class="token punctuation">{</span>
   <span class="token keyword">var</span> temp <span class="token operator">=</span> <span class="token number">0</span>

   <span class="token comment">// Store the sum of even numbers</span>
   <span class="token keyword">var</span> sum <span class="token operator">=</span> <span class="token number">0</span>

   <span class="token comment">// Initial two values of fibonacci sequence</span>
   <span class="token keyword">var</span> n1 <span class="token operator">=</span> <span class="token number">0</span>
   <span class="token keyword">var</span> n2 <span class="token operator">=</span> <span class="token number">1</span>
   <span class="token keyword">while</span><span class="token punctuation">(</span>n2 <span class="token operator"><</span> num<span class="token punctuation">)</span><span class="token punctuation">{</span>
      
      <span class="token comment">// Checking for even numbers</span>
      <span class="token comment">// By calculating their remainder if the remainder is 0</span>
      <span class="token comment">// then the number is number is even if not</span>
      <span class="token comment">// then the number is not even</span>
      
      <span class="token keyword">if</span> <span class="token punctuation">(</span>n2 <span class="token operator">%</span> <span class="token number">2</span> <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
         sum <span class="token operator">+=</span> n2
      <span class="token punctuation">}</span>
      <span class="token comment">// Adding two previous numbers to find ith</span>
      <span class="token comment">// number of the series</span>
      temp <span class="token operator">=</span> n1
      n1 <span class="token operator">=</span> n2
      n2 <span class="token operator">+=</span> temp
   <span class="token punctuation">}</span>
   <span class="token keyword">return</span> sum
<span class="token punctuation">}</span>
<span class="token function">print</span><span class="token punctuation">(</span><span class="token string">"Sum of even fibonacci terms:"</span><span class="token punctuation">,</span> <span class="token function">SumOfEvenFibonacci</span><span class="token punctuation">(</span>num<span class="token operator">:</span> <span class="token number">100</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

Sum of even fibonacci terms: 44

Here, in the above code, we create a function named SumOfEvenFibonacci() to find the sum of even fibonacci terms. In this function, we find the fibonacci ser ies by adding two previous numbers and then check for all the numbers of fibonacci series starting from 0 to 100 for even numbers and then find the sum of even numbers using the following code:

<span class="kwd">while</span><span class="pun">(</span><span class="pln">n2 </span><span class="pun"><</span><span class="pln"> num</span><span class="pun">){</span><span class="pln">
   </span><span class="kwd">if</span><span class="pln"> </span><span class="pun">(</span><span class="pln">n2 </span><span class="pun">%</span><span class="pln"> </span><span class="lit">2</span><span class="pln"> </span><span class="pun">==</span><span class="pln"> </span><span class="lit">0</span><span class="pun">){</span><span class="pln">
      sum </span><span class="pun">+=</span><span class="pln"> n2
   </span><span class="pun">}</span><span class="pln">
   temp </span><span class="pun">=</span><span class="pln"> n1
   n1 </span><span class="pun">=</span><span class="pln"> n2
   n2 </span><span class="pun">+=</span><span class="pln"> temp
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">return</span><span class="pln"> sum</span>

Working of the above code is :

<span class="pln">temp </span><span class="pun">=</span><span class="pln"> </span><span class="lit">0</span><span class="pln">
sum </span><span class="pun">=</span><span class="pln"> </span><span class="lit">0</span><span class="pln">
n1 </span><span class="pun">=</span><span class="pln"> </span><span class="lit">0</span><span class="pln">
n2 </span><span class="pun">=</span><span class="pln"> </span><span class="lit">1</span><span class="pln">
num </span><span class="pun">=</span><span class="pln"> </span><span class="lit">100</span><span class="pln">
</span><span class="kwd">while</span><span class="pun">(</span><span class="lit">1</span><span class="pln"> </span><span class="pun"><</span><span class="pln"> </span><span class="lit">100</span><span class="pun">){</span><span class="pln">
   </span><span class="kwd">if</span><span class="pln"> </span><span class="pun">(</span><span class="lit">1</span><span class="pln"> </span><span class="pun">%</span><span class="pln"> </span><span class="lit">2</span><span class="pln"> </span><span class="pun">==</span><span class="pln"> </span><span class="lit">0</span><span class="pun">)</span><span class="pln"> </span><span class="pun">=></span><span class="pln"> </span><span class="pun">(</span><span class="lit">1</span><span class="pln"> </span><span class="pun">==</span><span class="pln"> </span><span class="lit">0</span><span class="pun">)</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> condition </span><span class="kwd">false</span><span class="pun">{</span><span class="pln">
      sum </span><span class="pun">+=</span><span class="pln"> n2
   </span><span class="pun">}</span><span class="pln">
   temp </span><span class="pun">=</span><span class="pln"> </span><span class="lit">0</span><span class="pln">
   n1 </span><span class="pun">=</span><span class="pln"> </span><span class="lit">1</span><span class="pln">
   n2 </span><span class="pun">=</span><span class="pln"> </span><span class="lit">1</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> </span><span class="lit">0</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="lit">1</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">while</span><span class="pun">(</span><span class="lit">1</span><span class="pln"> </span><span class="pun"><</span><span class="pln"> </span><span class="lit">100</span><span class="pun">){</span><span class="pln">
   </span><span class="kwd">if</span><span class="pln"> </span><span class="pun">(</span><span class="lit">1</span><span class="pln"> </span><span class="pun">%</span><span class="pln"> </span><span class="lit">2</span><span class="pln"> </span><span class="pun">==</span><span class="pln"> </span><span class="lit">0</span><span class="pun">)</span><span class="pln"> </span><span class="pun">=></span><span class="pln"> </span><span class="pun">(</span><span class="lit">1</span><span class="pln"> </span><span class="pun">==</span><span class="pln"> </span><span class="lit">0</span><span class="pun">)</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> condition </span><span class="kwd">false</span><span class="pun">{</span><span class="pln">
      sum </span><span class="pun">+=</span><span class="pln"> n2
   </span><span class="pun">}</span><span class="pln">
   temp </span><span class="pun">=</span><span class="pln"> </span><span class="lit">1</span><span class="pln">
   n1 </span><span class="pun">=</span><span class="pln"> </span><span class="lit">1</span><span class="pln">
   n2 </span><span class="pun">=</span><span class="pln"> </span><span class="lit">1</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> </span><span class="lit">1</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="lit">2</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">while</span><span class="pun">(</span><span class="lit">2</span><span class="pln"> </span><span class="pun"><</span><span class="pln"> </span><span class="lit">100</span><span class="pun">){</span><span class="pln">
   </span><span class="kwd">if</span><span class="pln"> </span><span class="pun">(</span><span class="lit">2</span><span class="pln"> </span><span class="pun">%</span><span class="pln"> </span><span class="lit">2</span><span class="pln"> </span><span class="pun">==</span><span class="pln"> </span><span class="lit">0</span><span class="pun">)</span><span class="pln"> </span><span class="pun">=></span><span class="pln"> </span><span class="pun">(</span><span class="lit">0</span><span class="pln"> </span><span class="pun">==</span><span class="pln"> </span><span class="lit">0</span><span class="pun">)</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> condition </span><span class="kwd">true</span><span class="pun">{</span><span class="pln">
      sum </span><span class="pun">=</span><span class="pln"> sum </span><span class="pun">+</span><span class="pln"> n2 </span><span class="pun">=></span><span class="pln"> sum </span><span class="pun">=</span><span class="pln"> </span><span class="lit">0</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> </span><span class="lit">2</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="lit">2</span><span class="pln">
   </span><span class="pun">}</span><span class="pln">
   temp </span><span class="pun">=</span><span class="pln"> </span><span class="lit">1</span><span class="pln">
   n1 </span><span class="pun">=</span><span class="pln"> </span><span class="lit">2</span><span class="pln">
   n2 </span><span class="pun">=</span><span class="pln"> </span><span class="lit">2</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> </span><span class="lit">1</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="lit">3</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="pun">...</span><span class="pln"> so on till num </span><span class="pun">=</span><span class="pln"> </span><span class="lit">100.</span>

Now we call the function and pass 100 as an argument and display the sum that is 44(2+8+34 = 44).

Example 2

The following program shows how to find the sum of even fibonacci terms till number N.

<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">// Function to find the sum of even fibonacci terms</span>
func <span class="token function">SumOfEvenFibonacci</span><span class="token punctuation">(</span>num<span class="token operator">:</span> Int<span class="token punctuation">)</span> <span class="token operator">-</span><span class="token operator">></span> Int<span class="token punctuation">{</span>

   <span class="token keyword">var</span> temp <span class="token operator">=</span> <span class="token number">0</span>
   <span class="token keyword">var</span> sum <span class="token operator">=</span> <span class="token number">0</span>
   <span class="token keyword">var</span> n1 <span class="token operator">=</span> <span class="token number">0</span>
   <span class="token keyword">var</span> n2 <span class="token operator">=</span> <span class="token number">1</span>
	
   <span class="token keyword">while</span><span class="token punctuation">(</span>n2 <span class="token operator"><</span> num<span class="token punctuation">)</span><span class="token punctuation">{</span>
	
      <span class="token comment">// Checking for even numbers</span>
      <span class="token keyword">if</span> <span class="token punctuation">(</span>n2 <span class="token operator">%</span> <span class="token number">2</span> <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
         sum <span class="token operator">+=</span> n2
      <span class="token punctuation">}</span>
	
      <span class="token comment">// Adding two previous numbers to find ith</span>
      <span class="token comment">// number of the series</span>
      temp <span class="token operator">=</span> n1
      n1 <span class="token operator">=</span> n2
      n2 <span class="token operator">+=</span> temp
   <span class="token punctuation">}</span>
   <span class="token keyword">return</span> sum
<span class="token punctuation">}</span>
<span class="token comment">// Taking input from the user</span>
<span class="token function">print</span><span class="token punctuation">(</span><span class="token string">"Please enter the value:"</span><span class="token punctuation">)</span>
<span class="token keyword">var</span> val <span class="token operator">=</span> <span class="token function">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 comment">// Calling function</span>
<span class="token keyword">var</span> res <span class="token operator">=</span> <span class="token function">SumOfEvenFibonacci</span><span class="token punctuation">(</span>num<span class="token operator">:</span> val<span class="token punctuation">)</span>
<span class="token function">print</span><span class="token punctuation">(</span><span class="token string">"Sum of even fibonacci terms are:"</span><span class="token punctuation">,</span> res<span class="token punctuation">)</span>
</div>

STDIN Input

Please enter the value:
10000

Output

Sum of even fibonacci terms are: 3382

Here, in the above code, we creat e a function named SumOfEvenFibonacci() to find the sum of even fibonacci terms. Here we take the input from the user and pass this input in the SumOfEvenFibonacci() function as an argument. Suppose user enter the number 10000 so the total sum of even numb ers present from 0 to 10000 is 3382.