chapter 4 : programming

• to vary what a program does you use a conditional structure
• conditional structure is also called an ‘if’ structure
• in a conditional structure, it starts with the word ‘if’ and then has a logical test
• the logical test can be true or false
• a logical test uses operators to compare values
• a logical test usually compares two values 


  it uses relational operator to compare the two values
• relational operators are used to compare numbers
• operators and what it means

  == equal to

  != not equal to

  > greater than

  < less than

  >= greater than or equal to

  <= less than or equal to
• The word ‘if’ is a python key word
• in most programming languages, every loop has an exit condition
• the exit condition is how you stop the loop
• there are two types of loops:

  • a counter loop (or fix loop) repeats a set, number of times and stops
  • a conditional loop (or condition control loop) is controlled by a logical test
• a counter loop is called a for loop
• another name for counter loop is fixed loop because the commands inside the counter loop repeat a fixed number of times. you set the number of repeats on the top of the loop.
• conditional loop:

  the loop will repeat until the condition is true: this is in scratch

  • if the condition is false, the loop will continue
  • if the condition is true, the loop will stop
• use a loop when you want to repeat commands inside a program
• if you know exactly how many times do you want to repeat the commands, use a counter loop
• If you don’t know exactly how many times you want to repeat the command, use a conditional loop
• in python a conditional loop is called a while loop
• conditional loop:

  the loop will repeat until the condition is true: this is in python

  • if the condition is false, the loop will stop
  • if the condition is true, the loop will countinue
• the rules of a programming language are called syntax


  if you break the rules of a programming language, you make a syntax error
• translating : the computer turns the commands into machine code


  running : the computer executes the machine code commands
• Program commands the handle inputs and outputs are called interface
• comment explains what each section of the program is designed to do
• The rules of the language, such as the rules of a programming language is known as syntax
• The counter looping statement repeats a set number of times then stops
• the program is readable if it is easy to understand
• a syntax error is a type of error that breaks the rules of a programming language