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What is an Algorithm?

In this tutorial, we will learn what algorithms are with the help of examples.

An algorithm is a set of well-defined instructions in sequence to solve a problem.


Qualities of a good algorithm

  1. Input and output should be defined precisely.
  2. Each step in the algorithm should be clear and unambiguous.
  3. Algorithms should be most effective among many different ways to solve a problem.
  4. An algorithm shouldn't include computer code. Instead, the algorithm should be written in such a way that it can be used in different programming languages.

Algorithm Examples

Algorithm to add two numbers

Algorithm to find the largest among three numbers

Algorithm to find all the roots of the quadratic equation

Algorithm to find the factorial

Algorithm to check prime number

Algorithm of Fibonacci series


Examples Of Algorithms In Programming

Algorithm to add two numbers entered by the user

Step 1: Start
Step 2: Declare variables num1, num2 and sum. 
Step 3: Read values num1 and num2. 
Step 4: Add num1 and num2 and assign the result to sum.
        sum←num1+num2 
Step 5: Display sum 
Step 6: Stop

Find the largest number among three different numbers

Step 1: Start
Step 2: Declare variables a,b and c.
Step 3: Read variables a,b and c.
Step 4: If a > b
           If a > c
              Display a is the largest number.
           Else
              Display c is the largest number.
        Else
           If b > c
              Display b is the largest number.
           Else
              Display c is the greatest number.  
Step 5: Stop

Roots of a quadratic equation ax+ bx + c = 0

Step 1: Start
Step 2: Declare variables a, b, c, D, x1, x2, rp and ip;
Step 3: Calculate discriminant
         D ← b2-4ac
Step 4: If D ≥ 0
              r1 ← (-b+√D)/2a
              r2 ← (-b-√D)/2a 
              Display r1 and r2 as roots.
        Else     
              Calculate real part and imaginary part
              rp ← -b/2a
              ip ← √(-D)/2a
              Display rp+j(ip) and rp-j(ip) as roots
Step 5: Stop             

Factorial of a number entered by the user.

Step 1: Start
Step 2: Declare variables n, factorial and i.
Step 3: Initialize variables
          factorial ← 1
          i ← 1
Step 4: Read value of n
Step 5: Repeat the steps until i = n
     5.1: factorial ← factorial*i
     5.2: i ← i+1
Step 6: Display factorial
Step 7: Stop

Check whether a number is a prime number or not

Step 1: Start
Step 2: Declare variables n, i, flag.
Step 3: Initialize variables
        flag ← 1
        i ← 2  
Step 4: Read n from the user.
Step 5: Repeat the steps until i=(n/2)
     5.1 If remainder of n÷i equals 0
            flag ← 0
            Go to step 6
     5.2 i ← i+1
Step 6: If flag = 0
           Display n is not prime
        else
           Display n is prime
Step 7: Stop 

Find the Fibonacci series till term ≤ 1000.

Step 1: Start 
Step 2: Declare variables first_term,second_term and temp. 
Step 3: Initialize variables first_term ← 0 second_term ← 1 
Step 4: Display first_term and second_term 
Step 5: Repeat the steps until second_term ≤ 1000 
     5.1: temp ← second_term 
     5.2: second_term ← second_term + first_term 
     5.3: first_term ← temp 
     5.4: Display second_term 
Step 6: Stop