Computer

• Computer program


  A set of instructions a computer uses to solve a problem
• Computer program


  Directs the computer to perform the actions needed to arrive at a solution
• WHAT IS MEANT BY ‘PROBLEM’?

  A problem is something that needs to be solved or a task that needs to be accomplished.
• HOW SHOULD YOU DESIGN PROGRAMS?

  There are two main phases in program design:

  The Problem-Solving Phase: Done without the use of a computer

  The Implementation Phase: The designs developed during the problem-solving phase are executed on the computer.
• WHAT IS AN ALGORITHM?

  An algorithm is a formal sequence of instructions that defines a solution to a

  problem. The ‘a’ is emphasized because a problem could have multiple solutions.
• THE FIVE MAIN PROBLEM-SOLVING STEPS

  Whenever attempting to solve a problem, there are certain steps that should be followed. They are:

  Define the problem

  Propose and evaluate solutions

  Determine the most efficient solution

  Represent the most efficient solution in the form of an algorithm

  Test the algorithm
• PROBLEM STATEMENT (a clear definition of the problem that needs to be solved)
• INPUT – the data you are provided with or have to obtain from the user. Some words that help you to identify the input are: read, input, enter, given, accept
• OUTPUT – the results that should be produced
• PROCESSING – the tasks that must be performed, i.e. what must be done

  with the input to get the output
• STORAGE – the data that must be stored
• A VARIABLE is a name that is given to represent a piece of data that is unknown can be changed/varied while a program is running.
• A VARIABLE can be changed/varied while a program is running.
• Declaring a variable lets the computer know ahead of time what type of data it is allowed to hold. That way, the computer can make sure a user does not enter invalid data
• RULES you must follow when naming variables:

  The name must not contain a space.

  A variable name must only contain LETTERS, DIGITS and UNDERSCORES (_).

  A variable name MUST begin with a letter.

  You cannot use a RESERVED WORD as a variable name (PRINT, PROGRAM, INPUT, BEGIN, END, START, STOP, etc.).
• Variables are NOT Case Sensitive
• A CONSTANT is an IDENTIFIER (has an associated value)

  A CONSTANT consists of two things:a name,and a value.The name should clearly illustrate what the constant is all about, and the value is the actual value of the constant

  CONSTANTS are very useful when we want to set a value once, and then repeat it in many locations inside our program.
• CONSTANTS cannot be altered by a program during execution

  Example of CONSTANTS

  Pi =3.14

  The number of inches in a foot = 12

  The number of days in a week = 7

  The number of months in a year = 12

  CONSTANTS cannot be altered by a program during execution
• INTEGER

  Positive and negative numbers which do NOT have a decimal point, e.g. -100, 0, 43
• REAL

  Positive and negative numbers that may have a decimal point, e.g. -7.2, 0.1987, 99.0
• CHARACTER

  A single character (letter, digit or symbol) e.g. A, Z, 9, 0, $, &, ?
• STRING

  A group of up to 255 characters
• BOOLEAN

  Either true or false (and nothing else)