Part 1, C++ program Structure

• Sematics and Syntax
  • Syntax is the set of rules coverning how structures are composed in a language.
  • Semantics are the rules for determining the meaning of structures composed in a language.
  • We will be concerned with learning the syntax of the C++ in the beginning.
  • This will shift as time goes by. (This is the beginning of programming)
  • Eventually we will be concerned with what we can do with any language. (This is computer science)
• Every C++ program looks somewhat like this

      #include <iostream>
      #include <string>
  
      using namespace std;
  
      const string PHRASE = "Hello World";
  
      int main () {
          string greeting;
  
          greeting = PHRASE + ", how are you?";
  
          cout << greeting << endl;
  
          return 0;
      }
      

• This program:
  • It has a single function, main
    • This function takes no input.
    • This function returns an integer, or an int
  • It uses a constant, PHRASE
    • This is a quantity which will no change throughout the program
    • has data type string or 0 or more characters
    • It is assigned the literal value "Hello World"
  • There is a single variable, greeting
    • This is also of data type string.
    • it is constructed by concatenating the value of the constant PHRASE with the string literal ", how are you?".
  • The program then prints the value of greeting
  • And returns a value of 0
• Notice:
  • Some portions are inportant syntaticaly and some are just style
    • Space, for the most part is not important, but it makes the program easier to read. Consider:

          #include <iostream>
          using namespace std;const string PHRASE
          ="Hello World";int main(){string greeting;greeting=PHRASE+
          ",how are you?";cout <<greeting<<endl;return 0;}
      	 

    • Space, or whitespace, includes
      • The space character
      • The tab character
      • The carrage return, or newline character.
    • We use space to make the program more readable
    • This is called programming style
    • My style is different from the book.
    • The style you choose is not important but
      • It must make sense and be readable
      • You should be consistant
      • You must follow any guidelines given to you.
      • More on this as we go along
    • In general
      • Put one instruction per line
      • Indent things between { and }
  • Punctuation
    • This is important.
    • In C++, the semicoln (;) tells the compiler that a command is complete
    • This is just like the period (.) in english.
    • Parenthesis () must match.
    • As must {}, "", and ''
    • {} (braces) are used to mark "units" within code.
    • "" are used to mark string literals
    • '' are used to mark character literals
  • Some parts we are not going to talk about now, just put them in
    • using namespace std;
  • Order is important.
    • #include <iostream> needs to be first
    • using namespace std; needs to be next.
    • We will learn more about this as we go along.
• Reserved Words
  • Some words, like int and return have meaning in C++
  • We will learn these as time goes by.
  • A full list of them are in appendix A, page 1011
  • int is the datatype integer, it means the thing that follows deals with integers
  • return stops execution of the current subprogram (or function) and returns execution to the calling program or function.
    • It can return a value (0 in our program)
    • Or it doesn't have to.
    • Much more on this later.
• Identifiers are names we associate with objects within our program
  • They can name data locations (variables and constants)
  • They can name subprograms (main)
  • They can name other things as well.
  • We will use them alot
  • Rules for constructing valid identifiers
    • They cannot be a reserved word
    • They must start with a letter
    • They can contain only letters, numbers and some special characters (_ but not -,+, or whitespace)
    • You can begin with a _ as well, but don't
  • Guidelines for constructing good identifier names
    • They should describe what you are using them for
    • Not too short, PMTV is not as good as PaymentValue
    • But not too long either
      • You must type them exactaly the same everywhere in the program
      • TheValueOfTheFuturePaymentFromClient seems somewhat too long.
    • Mix upper and lower case
      • The author likes to start vaiables with a lower case and each new word with an upper case
      • theFutureValue
      • Constants are usually in all upper case, and use a _ to seperate words: GREETING_STRING
• Data and Data Types
  • Computer memory is a place where data and programs are stored.
  • At the lowest level it is a collection of 0s and 1s
  • We interpret the contents of memory to be different things.
  • 0110 0001
    • Could be the letter 'a'
    • Or the number 61
    • Or the number .0625
  • When we write programs, we associate an area of memory with a variable.
  • That is where we store information
  • We need to know what we are storing, so we must provide the data type
  • Basic types include integers (int), non integer numbers (floats) single symbols (char), or boolean values (bool)
  • We also need to associate an identifier (or name) with memory locations.
  • When declaring a varaible, or allocating memory to hold a piece of information, use both an identifier and a data type.

    	     char middleInitial;
    	     int age;
    	     float income;
    	     bool married;
    	

  • If we want to declare multiple variables of the same type we can:

    	         char firstInitial, middleInitial, lastInitial;
    		 int day, year;
    		 float grossPay, netPay, deductions, taxRate;
    	     

  • Declarations of this type set aside a chunk of memory.
  • They do NOT place a value in that chunk of memory.
• Basic Output
  • This is not part of the C, C++ language
  • You need to link with a library to do this
  • But the library for this is automaticaly linked with your program
  • But this is the reason for the #include <iostream> at the top of the program.
  • cout is an output stream. You place values in it.
  • << is the stream insertion operator or put to
  • put to will take what is on the right hand side and put it in the stream on the left hand side.

    	      cout   <<       5;
                   LHS operator  RHS
    	 

  • Will eventually print the number 5.
  • But the machine will buffer this output, so we need to flush the buffer.
  • endl is a function that produces the end of line marker, and flush the buffer.

    	      cout << 5;
    	      cout << endl;
    	 

  • We do this often enough that C++ provides a shortcut

    	      cout << 5 << endl;
    	 

  • This will print the number 5, then print the end of line character.
  • It is performed from left to right.
• Character Data
  • type char can hold a single character
  • This is anything from the ascii character set
  • It is 8 bits.
  • letter, digit, special character

    	char x;
    	

  • Declares a variable named x that will hold a character

    	char aLetterForYou;
    	

  • There are limited operations on characters.
  • But you can output them

    	     cout << aLetterForYou <<
    	

  • Will print the value that is stored in aLetterForYou
  • Literal character data is given with single quotes 'a' represents the letter a.
  • An assignment statement takes what is on the right hand side and stores it in the left hand side.
  • It is done with the = operator.

     
    	    char a, aLetter;
    
    	    a = 'q';
    	    aLetter = a;
    	    cout << aLetter << endl;
    	

  • Write a program that will print out your initials. Store each initial in its own variable.
• Strings
  • Strings are collections of characters.
  • They are not part of C++, but part of the standard library.
  • You need to add the line #include <string> at the top of your program.
  • The data type is string
  • Litterals are surrounded with quotation marks "

    	    string firstName;
    
    	    firstName = "Dan";
    	    cout << firstName << endl;
    	

  • Literals may not contain a new line character.

    	    string fullName;
    
    	    fullName = "Dan
    	                 Bennett";
    	

  • Is not permitted;
  • but the empty string "" is.
  • Concatenation is an operation on strings
    • +
    • string1 + string2 produces a new string containing string1 followed by string 2.

      	    string firstName;
      	    string lastName;
      	    string fullName;
      
      	    firstName = "Dan";
      	    lastName = "Bennett";
      	    fullName = firstName + lastName;
      	    cout << fullName << endl;
      	    

  • Write a program that will print all of the permutations of a person's name.
• Program Execution
  • Programs start with the main function
  • Each statement is executed
    • From top to bottom
    • From left to right
  • This is the flow of execution.
  • Order of statements matter.
• Documentation
  • Anything following a // is ignored by the compiler until the next carrage return
  • Anything following /* is ignored until a */ is found
  • Including other /*

    	// Variables to hold the user's name
    	string firstName,      // The first name
    	       middleName,     // Middle Name of the person
    	       lastName;       // The last name of the user
    
    	/**********************************************************
    	*  We will now print the user's name                      *
    	**********************************************************/