Programming Basics

Programming Basics

1. Data Types

   • Programming languages have Five Main Data Types
   • Each data types is allocated to a different amount of memory
   • Using the correct data types makes code more memory more efficient, robust (hard to break) and predictable
   • Casting is used to change the Data Type
   • Languages have functions that let you manually convert between data types - this is known as casting. This can be done using the int() / float() / bool() / str() commands
     • int("1")
       • Converts the string "1" to the integer 1
     • float(1)
       • Converts the integer 1 to the float 1.0
     • bool(1)
       • Converts the integer 1 to the Boolean value True
     • str(True)
       • Converts the Boolean value True to the string "True"
   • It's important to realise that the integer 1, the real 1.0 and the strings "1" and "1.0" are all different
   • You can also find the ASCII number of characters and vice versa using ASC() and CHR() functions
     • ASC("b")
       • Converts the character "b" into its ASCII number 98
     • CHR(98)
       • Converts the ASCII number 98 into its equivalent character "b"
   • Using the Correct data types for different variables

2. Strings

   • Strings are written inside Quotation Marks
     • Strings can be joined together to form new strings - this is called concatenation. It's often done using + operator
     • Strings are usually written inside double quotation marks ", but sometimes single quotes are used '.
   • Programs let you Manipulate Strings in a variety of ways
     • Characters in a string are usually numbered starting at zero
     • x.upper
       • Changes all characters in string x to upper case
         • HELLO
     • x.lower
       • Changes all characters in string x to lower case
         • hello
     • x.length
       • Returns the number of characters in string x
         • 5
     • x[i]
       • Extracts the character position I from string x
         • x[1] = e
     • x.subString(a,b)
       • Extracts a string starting at position a with length b from string x
         • x.subString(3,2) = lo
   • Example - An electricity company generates a customer's 7 character username from:
     • 1. the first 3 letters of their town as uppercase letters
       • 2. the customer's age when they sign up (2 digits)
         • 3. the first letter and last letters of the customer's surname as lowercase letters
   • Strings are a data type made up of characters

3. Program Flow

   • IF statements usually have an IF-THEN-ELSE structure
     • IF statements allow you to check if a condition is true or false, and carry out different actions depending on the outcome. You can think about them as a flow diagram.
     • If there is nothing for the program to do when the condition is false, leave out the ELSE part.
   • Nested IF statements allow multiple outputs
     • More complex IF statements can be made by putting one IF statement inside another one - this type of selection statement is called a nested IF statement.
     • Nested IF statements allow you to check more conditions once you've established that the previous condition is true.
     • IF-ELSEIF statements can also be used to check multiple conditions. They are different from nested IF statements as they only check more conditions if the previous condition is false