Computer languages

• When you learn to program you learn skills that allow you to adapt to use other languages very quickly.
• By the time I had left school I knew a total of three languages well. But by the time I started university a few months later I knew a total of eight languages well.

• There are many different programming languages out there. Learning one programming language makes it easy to learn another language, but programming languages all serve different purposes.
• For example, FORTRAN was developed before spreadsheets existed and was an excellent language for calculations.
• Python is often used in research projects because of its simplicity to write and decent performance.
• Java is often used for programs that work on multiple computer operating systems.
• PHP is often used for web programming because of its web –oriented features.

• In one of the first lessons on computer programming, we said that a computer program is a series of instructions.
• Continuing this idea, a computer see programs as a series of codes that it can understand. This is called machine code.
• Back when computers were in their infancy, people wrote computer programs using punch cards.
• These days, computers work electronically on a series of switches which are represented by 1s and 0s called binary.

• Punch cards were very simple - if there was a hole then it was a 1, if there wasn’t a hole then it was a 0.
• This was how computer programs were stored and rerun.
  

• Computer systems use electronic components such as the RAM and CPU.
• These components are made up of series of switches called transistors.
• When a computer program is run, it instructs the computer to switch on certain transistors.

• These transistors represent a 1 or 0 based on whether they are switched on.
• For this reason, computer systems are known as two–state machines.
• A computer can then execute (run) them as a computer program and perform actions based on their state.

• When we write programs in Visual Basic, Python or JavaScript, we are writing the series of instructions needed for a computer to be able to do something.
• A computer system cannot really see a Visual Basic or Python program as a series of computer instructions.
• A computer needs to have it as a series of 1s and 0s to understand it. To do this, a translator is required.

• A computer program is categorised as either high-level or low-level.
• A high-level language is one that is written in English or near to English using words such as ‘if’, ‘loop’ whereas a low-level language is written in either machine code (such as 1s and 0s) or assembly code (MV x y) and very unlike the English language and difficult to read.
• Visual Basic, Python, JavaScript etc. are high-level languages.
• x86-64 Assembly (Intel) and machine code are low-level languages

• Assembly code is very short (often three letter words) that tell the computer what to. Instead of writing x = 10, you would write

MOV 10, x

• CPUs all have different assembly languages too. So, writing a program in assembly language and then trying to run it on another computer is not always going to work!
• Therefore, abstraction became a big thing in computer programs.

• Abstraction is all about adding layers on top of other layers. 
• These layers make it easier for us to write code, for example in Python we write x = 65 in assembly we write 

• It requires a lot more as you go further down the chain. 

• Also, since high-level programming languages are simply code, we can often run this on several computers if the computer can do the translation to machine code on the computer running the code!
• To do this, we have a small program called a runtime. The end user must have this runtime to run your code. The runtime translates the code whenever the program is run. Python uses a runtime system.
• Every time a layer is developed on top of another layer, for example all high-level languages are written in either low-level languages (such as assembly) or another high-level language (such as C++) they become slower than the layer below them. In other words, programs written in low-level languages run faster than those written in high-level languages.

• A compiler turns the users code into something that the computer understands in one go.
• Compilers check for bugs in the code, but they are more difficult to detect with a compiled program because the compiler only displays all the bugs at the end of the program compiling.
• Compiling can be slow, however. Some compilers can take several hours or days to compile a program.
• When a program is compiled, its original code is almost impossible to go back to (or decompile) and in terms of safety a compiled program is much better.

• An interpreter translates each line of code, line by line.
• If there is a bug in the code it will stop at the line where the bug is and inform the user.
• Interpreted programs are slower than compiled programs but do offer more tools to help find any problems in the code.