Basic Programming

• This is section 1.3 of the book.
• Programs start out as source code.
  • This is a set of instructions in a programming language.
• To create this you must know the language
  • The syntax or the words, symbols and rules for combining those in the appropriate programming language.
  • The semantics or the meaning of these words and symbols.
• If you look at English, we have a syntax rule that each sentence should have a subject, a verb, and an object. "Cows eat grass."
  • As humans we are able to deal with sentences that do not follow the rules.
  • As long as the sentences are close to the rules.
  • Computers are not yet able to do so.
• When you violate a syntax rule, you produce a syntax error.
  • Generally, the computer can tell you when a syntax error occurs.
  • Frequently it will describe the error and provide a possible solution.
  • These are difficult at first, but soon become commonplace.
• You can make a syntactically correct sentence that does not make sense
  • "The cow drives the car."
  • This is proper grammar (I hope) but the meaning is nonsense.
• In programming we will call these logical errors, or logic errors.
  • The computer is not capable of detecting logic errors.
  • This is up to the programmer, QA team, users, ...
  • These remain the bane of computer programmers and users.
• Programming Languages
  • There are many programming languages.
    • If you take theory of languages or compilers you should be able to design and implement your own language if you wish.
    • Many people have.
  • Languages can serve different purposes.
    • Designed for systems implementation (C++)
    • Designed for security (RUST)
    • Designed for wide availability (JAVA)
    • Teaching Language (PASCAL)
    • and many others.
• There are several basic types of programming languages
  • Low Level: Machine language or assembly.
    • These are very close to the hardware.
    • When you change processors, (intel, atom, ....) you change languages
    • These are somewhat difficult for humans to learn.
  • High Level: most of the languages you will encounter.
    • These are designed for humans to write and understand.
    • These are generally similar, we will see this as time goes by.
  • Special purpose:
    • These are generally high level, but have a special purpose.
    • SQL : Structured Query Language
      • Designed for searching databases.
    • HTML: Hypertext Markup Language
      • Designed for specifying linked document (web page) layout.
• You will learn multiple high level general purpose languages in your life
• You will probably also learn a set of special purpose languages.
• You will be exposed to machine and assembly languages.
• Changing from a high level language to machine language can be done in several ways.
  • A compiler is a program that takes a high level language and translates it into machine language all at one time.
    • Think of translating a book from one language to another.
    • It is a long process, but after it is finished you don't need to do it again.
    • This is efficient when you have code you will run many times.
    • It is slower when you run the code once.
  • An interpreter interprets and executes the code one line at a time.
    • Think of translating a speech as it occurs.
    • Hear a sentence, convert it to another language.
  • There are other ways to do this.
    • Notably java compiles to a machine independent code.
    • This code is interpreted by the JVM (Java Virtual Machine)
• These topics are covered more completely as we move through programming.