Algorithms

Algorithm

An algorithm is an effective method expressed as a finite list of well defined instructions for calculating a function, starting from an initial state and initial input. The instructions describe a computation, which will eventually produce output, when executed. We can use algorithm to solve any kind of problems. However, before writing a program, we need to write the steps to solve the problem in simple English language. This step-by-step procedure to solve the problem is called algorithm.

Example

Let us take one simple day-to-day example by writing algorithm for making "Maggi Noodles" as a food.

Step 1: Start

Step 2: Take pan with water

Step 3: Put pan on the burner

Step 4: Switch on the gas/burner

Step 5: Put magi and masala

Step 6: Give two minutes to boil

Step 7: Take off the pan

Step 8: Take out the magi with the help of fork/spoon

Step 9: Put the maggi on the plate and serve it

Step 10: Stop.

Further, the way of execution of the program shall be categorized into three ways: (i) sequence statements; (ii) selection statements; and (iii) iteration or looping statements. This is also called as "control structure".

Sequence statements: In this program, all the instructions are executed one after another.

Example

Write an algorithm to print "Good Morning".

Step 1: Start

Step 2: Print "Good Morning"

Step 3: Stop

Example

Write an algorithm to find area of a rectangle.

Step 1: Start

Step 2: Take length and breadth and store them as L and B?

Step 3: Multiply by L and B and store it in area

Step 4: Print area

Step 5: Stop

In the above mentioned two examples (Example II and III), all the instructions are executed one after another. These examples are executed under sequential statement.

Selective Statements: In this program, some portion of the program is executed based upon the conditional test. If the conditional test is true, compiler will execute some part of the program, otherwise it will execute the other part of the program.

Example

Write an algorithm to check whether he is eligible to vote? (more than or equal to 18 years old).

Step 1: Start

Step 2: Take age and store it in age

Step 3: Check age value, if age >= 18 then go to step 4 else step 5

Step 4: Print “Eligible to vote” and go to step 6

Step 5: Print “Not eligible to vote”

Step 6: Stop

Example

Write an algorithm to check whether given number is +ve, -ve or zero.

Step 1: Start

Step 2: Take any number and store it in n.

Step 3: Check n value, if n > 0 then go to step 5 else go to step 4

Step 4: Check n value, if n < 0 then go to step 6 else go to step 7

Step 5: Print “Given number is +ve” and go to step 8

Step 6: Print “Given number is -ve” and go to step 8

Step 7: Print “Given number is zero”

Step 8: Stop

In the above mentioned examples IV and V, all the statements are not executed, but based upon the input, some portions of the algorithm are executed, because we have „true‟ or „false‟ situation in the program.

Iterative statements: In some programs, certain set of statements are executed again and again based upon conditional test. i.e. executed more than one time. This type of execution is called „looping or iteration‟.

Example

Write an algorithm to print all natural numbers up to "n".

Step 1: Start

Step 2: Take any number and store it in n.

Step 3: Store 1 in I

Step 4: Check I value, if I<=n then go to step 5 else go to step 8

Step 5: Print I

Step 6: Increment I value by 1

Step 5: Go to step 4

Step 8: Stop

In the above example, steps 4, 5, 6 and 7 are executed more than one time.

Python : Algorithms Program List