Overview of Programming and Problem Solving

• When we finish this chapter you should be able to
  • Understand what a computer program is
  • Understand what an algorithm is
  • Understand what a high-level programming language is
  • Explain the edit-compile-execute process
  • Discuss the basic stages involved in writing a computer program
  • Discuss common problem solving strategies.
• Some of this material you will cover in CSCI 125 as well, so we will be brief.
• You should read chapter 1 at this time.
  • Pay attention to terms and definitions, this is important.
• Overview of Programming
  • What is a computer?
    • A programmable electronic device that can store, retrieve and process data.
    • This might need to be modified in your life time, but it will do for now.
    • Note it is not a person, but it once was!
  • What is programming?
    • You might be familiar with programs at an event (play, sports event ...)
      • in some sense these are "instructions" for what will happen
    • A computer program is a sequence of instructions to be performed by a computer.
      • Written in a computer programming language (programming language)
      • By a computer programmer (or programmer)
      • Following an algorithm (hopefully)
  • What is an algorithm?
    • An algorithm is a set of instructions that solve a problem in a finite amount of time.
      • We will refine this as you go through CS.
    • To use a computer in this lab
      1. Remove all materials from the cut out area of the desk
      2. Locate the lever under the table, in the center
      3. Press this lever to open the top
      4. Lift the cover to the open position
      5. Slide the button at the front center of the laptop
      6. Open the laptop
      7. Press the power button in the upper right hand corner of the base of the laptop.
      8. Log in and use the computer
    • Sometimes we use a picture.
    • To go to lunch in Van Houten
      1. 
      2. Follow the red line.
    • We use algorithms to create programs
      • They are a plan or blueprint for what we want to do
      • We construct an algorithm then translate that into a programming language.
    • To convert from Fahrenheit to Celsius
      1. Read in the number (tempInF) in Fahrenheit
      2. Subtract 32 from tempInF
      3. Multiply the result by 5
      4. Divide the result by 9
      5. Output the final result.
    • Algorithms are not rules:
    • You will be writing algorithms for this class
      • I expect you to do your best when writing algorithms
      • The level of detail to include in an algorithm is tricky
        • Too much detail and you have code, this is not useful
        • Too little detail and you don't know what to do, this is not useful either.
        • It is a trade off that you learn to deal with eventually
        • For now, give me your best effort
  • They talk about the Waterfall method for writing program, but we will come back to that later.
    • Please look this over for now however.
  • What is a programming language
    • This is a somewhat involved process.
    • Computers, at the hardware level use Machine Language.
      • This is just a series of numbers.
      • But the computer is able to interpret these as instructions
      • Add, subtract, save, output.
      • Assume the following
        • There is an accumulator used by most instructions
        • There are four memory locations (0,1,2,3)

        • Code	Action
          100	Input a number to accumulator
          101	Output a number from accumulator
          102 N	Add the number from memory location N to the accumulator
          103 N	Subtract the number from memory location N to the accumulator
          104 N	Multiply the accumulator by the number from memory location N
          105 N	Divide the accumulator b y the number from memory location N
          106 N	Store the accumulator in memory location N
          107 N	Load the accumulator from memory location N
          108 M N	Store the constant M in memory location N

        • So the simple program might look like this

          108 32 1
          108 9  2
          108 5  3
          100 
          103 1
          104 3
          104 2
          102
          		       

        • This is very much simplified, but it gives you the idea.
    • As time went by a simple solution was derived, assembly language
      • Each instruction was given a mnemonic. 100 - became LOAD
      • Programs look more like this:

        INPUT 
        SUB 32
        MUL 5
        DIV 9
        OUTPUT
        		   

    • Assembly and Machine code are hard to work with, so higher level languages were invented.
    • There are many of these, we will focus on C++

      #include 
      
      using namespace std;
      
      int main() {
          float tempInF,
          tempInC;
      
          cout << "Enter the temperature in Fahrenheit" << endl;
          cin  >> tempInF;
          tempInC = (tempInF-32)*5/9;
          cout << "The temperature in Celsius is " << tempInC << endl;
      
          return 0;
      }
      
      	      

  • Programming transformation
    • source code, object code (program), executable
    • Source code is the code in a programming language
    • Object code is code that is machine language
    • Executable code is in the correct format for the program to run
    • An assembler is a program that translates from assembly code to machine code
    • A compiler is a program that translates from an high level programming language to object code.
    • As a secondary function, the compiler will identify syntax errors in a program.