Program Construction

• Every C++ program has some common elements.
  • No matter what you need to put these things in
  • So just start out with the, don't worry about other parts.
  • And I just lied, but ignore that fact.
• I will construct a program and talk about these elements.
  • Pay attention to EVERYTHING
  • spacing (between elements and between lines)
  • Capatalization
  • Punctuation
  • Everything else too.
• Unless I say otherwise, you need to know what each part does and why it is formatted that way.
• If you don't understand, ask
• #include <iostream>
  • This is called a preprocessor directive
  • It "adds" elements to the C++ language.
  • In this case, it adds input and output routines.
  • Ok, so this one is tough right now.
  • We will really learn about this in 230
  • We will have other includes, and I will talk about when to use them.
• using namespace std
  • If two people have the same name, a namespace helps us determin which we are talking about.
  • This is a convienence thing, you should use it.
  • We will really lean about this in 330
• int Square( int);
  • int is a reserved word.
    • It has a predefined meaning in the langague
    • There are a list of reserverd words in appendis A.
    • We will study reserverd words through 330 and beyond.
    • In this case, it is a data type
    • A data type is a specific set of values along with a set of operations on those values.
    • This is the data type for integers.
    • We will explore this more in chapter 3.
  • Square is an identifier
    • This is a name associated with a user definied object in a program.
    • Everything we "make" will have an associated identifier.
    • Syntax rules for declaring an identifier
      • Identifiers must begin with a letter or the underscore
      • They may only contain letters, underscore, or digits.
      • They may NOT be reserverd words.
    • There are conventions for declaring identifiers too.
      • Some are specific to the type of object being named.
      • But a global rule is that the identifier should have meaning.
  • Square is also a function name.
    • this is a small sub-program which performs a task.
    • In this case, it will square a number.
    • When declaring function names, we use the conventions:
      • Each word should start with an upper case letter.
      • All other letters should be lower case.
    • We will study functions further in chapters 8 and 9
  • (int ) is a parameter list
    • This says the the function Square takes a single parameter, an integer.
  • ; marks the end of a statement.
  • int Square(int); is also a function prototype
    • Don't worry about this until later
    • Except that it is defining a function
    • In C/C++ everything must be Declared or defined before it is used.
    • This tells the compiler how the function Square is used.
    • Again, this is chapter 8/9 material.
• int main()
  • Begins the definition of the main routine.
  • main is a standard identifier
    • Every C/C++ program expects a function called main. This is where execution begins.
    • main is not a reserverd word, but is in some sense already taken,
    • But you must declare it for every program.
• {
  • This is the beginning of a code block.
  • it ends with a matching }
  • A code block turns one or more statements into a single statement.
  • Placement:
    • Two choices, like in the book, or like I do it.
  • Convention:
    • Everything inside of a code block is indented by a standard amount.
  • More on this later.
• int theNumber;
  • This is a variable declaration.
  • it is in the form: datatype identifier;
  • There are other forms which we will discuss, but this will do for now.
  • A variable is a location in memory referenced by an identifier
    • Variables may change value throughout the program.
    • But there is ALWAYS a value in the variable.
    • This is an uninitialized varable, since we have not given it a value
    • It currently contains garbage.
  • Variables must be defined before they can be used.
  • Convention:
    • Variable names start with a lower case letter.
    • Each new word starts with an upper case letter.
    • That way we can easly tell a variable from a function.
• theNumber = 7;
  • This is the first executable statement.
  • That means that the computer actually performs some action based upon this statement.
  • It is also an assignment statement.
  • In this case, the expression on the right hand side is evaluated.
  • The value is then stored in the variable on the left hand side.
  • = is an operator
    • These also have special meaning.
    • The list of operators is in appendix b.
    • The presidence is in this table as well.
  • 7 is a literal constant
    • That is a constant written in the program.
  • The result of this operation is that a 7 is stored at theNumber
• cout << "The number is " << theNumber << endl;
  • This is an executable statement as well.
  • cout is a standard identifier.
    • It is an input stream (part of iostream)
    • It is usually associated with the monitor, but it can be other things.
  • << is a stream insertion operator.
    • It takes the item on the right and inserts it into the stream on the left.
  • "The number is "
    • Is a string literal constant.
    • A string is another data type.
    • It is a collection of characters.
    • It is enclosed in quotation marks.
  • theNumber is an expression
    • The value of the variable (theNumber) is retreived and printed out.
  • endl is a standard identifier
    • It is part of the iostream library
    • It prints en end of line marker.
    • And it also flushes the buffer.
• cout << "The square is " << Square(theNumber) << endl;