CSCI 1110 - C++ Lecture Notes
Chapter 2 - C++ Syntax and Semantics,
and the Program Development Process

C++ Program Structure

Syntax and Semantics

Programming Style - Names

C++ Data Types

Assignment Statements and Expressions

Output

C++ Program Structure

• Every C++ program consists of one or more functions.
  
  
#include <iostream.h>

int Square(int);
int Cube(int);

int main()
{

cout << "27 squared is "
     << Square(27) << endl;
cout << "27 cubed is "
     << Cube(27) << endl;
return 0;
}

int Square(int n)
{
   return n * n;
}

int Cube(int n)
{
   return n * Square(n);
}
 



• The output of this program is
  
  
27 squared is 729
27 cubed is 19683
 
• Every C++ function must have a function named main. Execution of the program begins with the main function.
  
  
• Each function begins with a function declaration such as
  
  
int Square(int n)
 
which specifies what the function's return type is, its name, and a list of parameters for the function.
 


• The block of statements enclosed in braces - { and } - form the body of a function, which are executed when the name of the function is used in an expression.

Syntax and Semantics

• Programming Language - a set of rules, symbols, and special words used to construct a computer program.
  
  
• Syntax - The formal rules govering how valid instructions are written in a programming language.
  
  
• Semantics - The set of rules that determines the meaning of instructions written in a programming language.
  
  
• Metalanguage - A language that is used to write the syntax rules for another language.
  
  
• Syntax Templates are a graphic metalanguage that we will use to define the C++ language. Appendix D, page A10-A29 contains the syntax templates for C++.
  
  
• Example - Decimal integers:

• Semantics of Syntax Diagrams:
  
  
1. The name of the item being defined is above the box.
   
   
2. The definition of the item is inside the box.
   
   
3. Whenever another syntactic name is used, an instance of that item must be present.
   
   
4. When an item is shaded (blue), it it optional.
   
   
5. When an item is followed by ellipsis (. . .), it can be repeated any number of times.
   
   
6. Combining the previous two rules, that means that a shaded item followed by ellipsis can be repeated zero or more times.
   
   
7. The brace indicates that one item is chosen from the list of items.
   
   
• Valid and invalid Decimal Integers:
  
  

• Example - MainFunction:

• Identifier - A name associated with a function or data object and used to refer to that function of data object.

• Valid and invalid Identifiers:

 

Expression	Valid?	Reason
a	Valid
sum_of_squares	Valid
2x	Not Valid	Must begin with a letter or underscore
x2	Valid
GetData	Valid
Get Data	Not Valid	Contains a space character
int	Not Valid	int is a reserved word

 


• Reserved word - an identifier that has special meaning in C++. A reserved word cannot be used as a programmer-defined identifier.
  
  
• Appendix A, page A1, contains a list of the C++ reserved words.
  
  
• C++ is case-sensitive - uppercase letters are different from lowercase letters.




    PRINTTOPPORTION
    printtopportion
    pRiNtToPpOrTiOn
    PrintTopPortion

are 4 different identifiers. 



• Identifiers are used to name objects in a C++ program. A declaration is a statement that associates an identifier with a data object, a function, or a data type so that the programmer can refer to that item by name.
  
  
• Variable - a location in memory, referenced by an identifier, in which a data value that can be changed is stored.

• Examples:
  
  
int nStudents, maxScore, average;
 
 which is equivalent to
 
int nStudents;
int maxScore;
int average;


• Constant - a value used in a program that does not change.
  
  
• Literals - constant values with are written in a program.
  
  

Examples:

12
114.5
'A'
"Go Eagles!"


• A Named Constant is a location in memory, referenced by an identifier, where a data value that cannot be changed is stored.

• Examples:

 
const float PI = 3.14159;
const int MAX = 100;
const char BLANK = ' ';

Programming Style - Names

• Programming Style consists of conventions that are used when writing programs that makes them easier to read and to understand.
  
  
• Capitalization Style Guidelines for Identifiers:
  
  
1. Variable names should begin with a lowercase letter and each successive word should be capitalized.




    lengthInMiles
    seconds
    nStudents 


2. Programmer-written functions and programmer-defined data types begin with a capital letter with each successive word capitalized.




    CalcPay(rate, hours, wages)
    Cube(27)
    MyDataType 


3. Named constants are written using all capital letters with each word being separated by underscores.




    PI
    UPPER_LIMIT
    MAX_LENGTH


• Identifier names should be carefully chosen. Confusing names, or names that are similar to other names, make the program more difficult to understand and can result in programming errors.

C++ Data Types

• Data Type - a specific set of data values along with a set of operations on those values.
  
  
• Overview of C++ data types:

• The integral data types store whole numbers. The number of bits allocated to each integral type and therefore their ranges are different for different computer systems.
  
  
• Typical integral type allocations:
  
  

Integral Type	Bytes	Range	Unsigned Range
char	1	-128 - 127	0 - 255
short	2	-32,768 - 32,767	0 - 65,535
int	2	-32,768 - 32,767	0 - 65,535
long	4	-2,147,483,648  - 2,147,483,647	0 - 4,294,967,295

 

• The char data type can store integers or characters:

    'A'  'a'  ' '  '+'  '?'  '\'' 



• The floating types also increas in size from float, double and long double.
  
  
• Floating values are written using two different formats:
  
  
1. Floating numbers can be written using a decimal point separating the integer part and the fractional part of the number.




1.0   3.14159  -27.5   .85 


2. Floating numbers can be written using a exponential notation that is equivalent to scientific notation. The number is written as in format 1 followed by the character E and an exponent.




1.0E4  0.314159E+1 -5E2   1E-1

Assignment Statements and Expressions

• Assignment Statement - a statement that changes the value of a variable.

• Examples:




    quizScore = 10;
    pay = hoursWorked * payRate;
    y = -b + x * slope;
 


• C++ provides a standard set of arithmetic operators:
  
  

• Unary Operator - an operator that has just one operand.




    x = -y;
    z = +5; 


• Binary Operator - an operator that has two operands.




    x = a - b;
    z = c / d;
    y = n % 5;


• Modulus operator examples:



int a = 10;
int b = 7;
int x;

x = a % b;    // result: 3
x = a % 2;    // result: 0
x = b % a;    // result: 7




• The increment and decrement operators can be used as prefix or postfix operators.
  
  
• Prefix increment (and decrement) is written before the variable. The variable is incremented (decremented) and the new value is used as part of the expression.



int a = 10;
int b = 12;
int c;

c = ++a + b;    // 11 is stored in a
                // and 23 is stored in b



• Postfix increment (and decrement) is written after the variable. The variable is incremented (decremented) and the old value is used as part of the expression.
  
  

 
int a = 10;
int b = 12;
int c;

c = a++ + b;    // 11 is stored in a
                // and 22 is stored in b

Output

• The result of computation can be displayed on the screen by using a special variable named cout along with the insertion operator (<<).
  
  

    cout << "Hello";
    cout << "The answer is ";
    cout << 3 * num;



• Output statement syntax diagram:

• Examples:



Assume that the variable i contains the value 2 and j contains 6.