Topic 7.1 Programming

Topic 7.1 Programming

1. High level languages

   • A high level language is a programming language that allows code to be written. It is similar to a natural human language, such as Welsh or English. Some programmers prefer to use high level programming languages as they are easier to understand, learn and program. Their commands are similar to natural languages like English or Welsh and identifiers can be long and meaningful.
     • • Basic • Java • Pascal • COBOL • C# • C++

2. Machine code

   • Machine code is the opposite of a high level language in that it does not resemble any natural language and is made up entirely of bit patterns (instructions or data) that can be executed directly by the CPU. Examples of machine code instructions are opcodes and operands. High level languages have to be converted into machine code before they can be executed by the CPU. For further discussion. Although highly uncommon, some programmers may wish to program directly in machine code. This is primarily done when programming device drivers or where a fast execution speed are critical.

3. Variables

   • In computer programming, a variable may be required to store data that can change. Variables are given identifiers (names) that should reflect the data being stored in them. An example of a variable is txt_FirstName. This variable has a self-documenting identifier, which implies the type of data being stored in it is text containing a person’s first name.
   • Local and Global
     • A local variable is a variable that is defined within a sub procedure and as such is only accessible from within that same sub procedure. This is known as its scope.
       • The advantage of defining a local variable over a global variable is that it is easier to track the changes to a variable and the reason for the changes when it is only used within a sub procedure.
     • A global variable is a variable that has a larger scope as it is defined globally and is therefore accessible from anywhere within a program.
       • An advantage of defining a global variable over a local variable is that sometimes it can be the most efficient way of ensuring that an important piece of data is accessible to all sub procedures, e.g. the details of the user currently logged into a program.
   • Static and dynamic
     • Each time a program is run, static variables are stored in a location in memory and have a lifespan that lasts the entire time that program is running. For example, if you assign the number 2.14 to a static variable (and do not change it), the static variable will still contain 2.14 the next time you run the sub procedure and until the whole program stops running.
     • Each time a dynamic variable is defined, it is assigned a new location in memory and has a lifespan that ends when the sub procedure in which it was defined ends. For example, if within a sub procedure you assign the number 2.14 to a dynamic variable (and do not change it) and the sub procedure ends, the next time you run that sub procedure the dynamic variable will no longer contain any value.

4. Constants

   • Constants are used in computer programming to store data that does not change. Constants are also given self-documenting identifiers that should reflect the data being stored in them. An example of a constant would be Pi = 3.14, as this is a self-documenting identifier that does not change.