Conditional Algorithm

Conditional algorithms have selection statements in them.  Their control structure is known as Selection Control Structure.

The first illustration is that of the if-then construct.
The second illustration is that of the if-then-else construct.

Examples:
1. If grade is 70 or more, output Pass.
2. If grade is 70 or more, output Pass; otherwise output Fail.

Example Problem:
Write an algorithm that determines and outputs if the average of a student allows him to pass or fail; the passing mark is 70.

Solution #1: if-then construct
Print "Enter the average of a student"
input avg
if avg >= 70 then
print "Pass"
end if
input key

Solution #2: if-then-else construct
Print "Enter the average of a student"
input avg
if avg >= 70 then
print "Pass"
else
print "Fail"
end if
input key

Now you try one:
Write an algorithm that prompts the user to enter the name and cost of two items.  The algorithm should calculate and output the total cost.  If the total exceeds $25.00 then offer a discount of 10%; otherwise a discount of 5%; show the new total after discount.

Algorithms

There are four types of algorithms:  Simple, Conditional, Loops and Arrays

Simple Algorithms - basic calculations
Conditional Algorithms - selection statements

Algorithms are series of instructions that rigorously defines the solution to a problem.

The attributes of an algorithm are:

1. Must be precise
2. Must be ambiguous
3. Must be finite
4. Must be done in a logical order

Example of given problem:

Write an algorithm that prompts the user to enter two grades, and shows the average of the two grades.

Indicators that it is a simple algorithm:  basic calculation of entering data, performing calculation, and outputting results.

Solution:

Print "Enter a grade"

Input grade1

Print "Enter another grade"

Input grade2

Let total = grade1 + grade2

Let avg = total / 2

Print "The average of two grades is", avg

Input key

Problem Solving Phase

Click on the link below for a short video about the five steps in the problem solving phase along with an important message.

Intro to Programming by Ms Young

Problem Solving Phase

The key to solving a problem is understanding what is being asked to do, logic how to do it, and get it done.

The Five (5) Steps in Problem Solving Phase

1. Define the problem
2. Find a solution
3. Evaluate alternate solutions
4. Choose the most efficient solution and write an algorithm
5. Test algorithm for correctness

To define the problem, programmers use a defining diagram, commonly referred to as an IPO table. 

Defining Diagram - a three column table that separates a given problem into Input, Processing, and Output.

The IPO table does not solve the problem; it simply outline the procedural steps.  Calculations are not shown in the table.  

Example of IPO Table

 

Problem: Calculate and output the total cost of three items.

Input	Processing	Output
Cost1 Cost2 Cost3	1.   Read Cost1, Cost2, Cost3 2.   Calculate Total 3.   Print Total	Total

Input

We have assigned a name (variable name) to each of the cost values that will be entered.

we will learn more about variables at a later point.

Processing

Each processing step is numbered.  

The processing steps are what steps the computer will have to do to solve the problem.

The first processing step is always to (read) the variables that are inputted.

The final processing step is always to display (or print) was is to be outputted.

Output

Anything that needs to be displayed or the result of what is being asked to solve

You try one...

Prepare the defining diagram for the following problem:  Calculate and output the average of two quiz grades.  (hint...there are four processing steps)