Fibonacci Series in C++ using Do-While Loop

Before going to the program first let us understand what is a Fibonacci Series?

Fibonacci Series:

Fibonacci series is nothing but a Series of Numbers which are found by adding the two preceding(previous) Numbers.

For Example,

0,1,1,2,3,5,8,13,21 is a Fibonacci Series of length 9.

For more understanding you can check out the following link:

https://www.mathsisfun.com/numbers/fibonacci-sequence.html

Program code to Display Fibonacci Series in C++:

#include<iostream.h>
#include<conio.h>

void main()
{
int n,f,f1=-1,f2=1;
clrscr();

cout<<"  Enter The Number Of Terms:";
cin>>n;

cout<<"  The Fibonacci Series is:";

do
{
f=f1+f2;
f1=f2;
f2=f;
cout<<"  \n"<<f;
n--;
}while(n>0);
getch();
}

Working:

• First the computer reads the value of number of terms for the Fibonacci series from the user.
• Then using do-while loop the two preceding numbers are added and printed.
• The loop continues till the value of number of terms.

Step by Step working of the above Program Code:

Let us assume that the Number of Terms entered by the user is 5.

1. It assigns the value of n=5.
2. Then the loop continues till the condition of the do-while loop is true.

2.1.    do

f=f1+f2         (f=-1+1)         So f=0

f1=f2             (f1=1)            So f1=1

f2=f               (f2=0)           So f2=0

print the value of “f” (ie. 0)

n – –               (n=n-1)         So n=4

n>0      (4>0), do-while loop condition is true

2.2.    do

f=f1+f2         (f=1+0)         So f=1

f1=f2             (f1=0)            So f1=0

f2=f               (f2=1)           So f2=1

print the value of “f” (ie. 1)

n – –               (n=n-1)         So n=3

n>0      (3>0), do-while loop condition is true

2.3.    do

f=f1+f2         (f=0+1)         So f=1

f1=f2             (f1=1)            So f1=1

f2=f               (f2=1)           So f2=1

print the value of “f” (ie. 1)

n – –               (n=n-1)         So n=2

n>0      (2>0), do-while loop condition is true

2.4.    do

f=f1+f2         (f=1+1)         So f=2

f1=f2             (f1=1)            So f1=1

f2=f               (f2=2)           So f2=2

print the value of “f” (ie. 2)

n – –               (n=n-1)         So n=1

n>0      (1>0), do-while loop condition is true

2.5.    do

f=f1+f2         (f=1+2)         So f=3

f1=f2             (f1=2)            So f1=2

f2=f               (f2=3)           So f2=3

print the value of “f” (ie. 3)

n – –               (n=n-1)         So n=0

n>0      (0>0), do-while loop condition is false

2.6.    It comes out of the do-while loop.

1. Thus the program execution is completed.