Token (Lexical Units) -
The smallest individual unit in a
program is known as a Token or a lexical unit.
C++
has following tokens-
Keywords
Identifiers
Literals
Punctuators
Operators
Keywords
A keyword is that
which has a special meaning, those are already been explained to the C++
language like cout, cin, for, if, else etc. These are the reserve keywords.
Identifiers
The identifiers are those which are used for giving a name
to a variable like a, b etc. These are used for naming variables, objects,
classes, functions, arrays etc. When we declare any variable then we specify a
Name so that identifiers are used.
C++ is case sensitive as it treats upper and lower case
characters differently.
Ex. myfile, MUFILE, _CHK, DATEq_
Literals (constants)
The term literals (constants) refer to the fixed value means
a Constant is that whose value is never changed at the end of the program.
Ex. int x=5;
Here the value of x remains 5 at the end of program. C++
allows several kinds of literals-
bool literal
integer constant
character constant
floating constant
string constant
1.Bool literal
The bool literal in C++ is used to represent one of the two
Boolean values i.e. true or false. Boolean true means value ‘1’ and false means
value ‘0’.
2. Integer constant
Integer constants are whole numbers without any fractional
part. C++ allows three types of integer constants-
Decimal(base 10)
Octal(base 8)
Hexadecimal(base 16)
3. Character Constants
A character constant is one character enclosed in single
quotes as in ‘z’. Single character constant eg. ‘c’ or ‘A’ has type ‘char’
which is a C++ data type for characters.
C++ allows
certain non graphic characters in character constants. Non- graphic characters are those characters that cannot be typed
directly from keyboard. Eg. Backspace, tabs etc.
4.Floating constant
Floating constants are also called real constants. Real constants are numbers having fractional
parts. These may be written in one of two forms called fractional form or
the exponent form.
Ex. 2.0, 17.5, -13.0,
-0.000625
5.String literals
A string literal is a sequence of characters surrounded by
double quotes. Each string is by default added with a special character ‘\0’
which makes the end of a line. Ex. “abc” size is 4.
Operators
An operator is a special symbol which is used for performing
an operation. So that operator is that which has a special meaning and also
have a sign.
Ex. We know that + is used for adding two numbers. There are
two types of operators -
1. Unary operator
2. Binary operator
Role of compiler
A compiler is a
program that translates human readable source code
into computer executable machine code. A part of compiler’s job is to analyze
the program code for “correction”. Compiler can certainly detect error in the
form of program. Some common form of program error are-
1.
Syntax error
Syntax error occurs when a grammatical rule
of C++ is violated.
Ex. main()
{
int a, b:
cin>>a>>b;
cout<<a+b’
return 0
}
In
the first and third line after main (), there is termination error. And the last
statement has missing (;).
2.
Semantics error
Sometimes error occurs when statements are
not meaningful. Semantics refer to the set of rules which give the meaning of a
sentence. Ex. The statement p*q=z; will
result in a semantic error.
3.
Type errors
Data in C++ has an associated data type
.The value 6, for instance, is an integer. ‘a’ is a character constant where as
“hi” is a string.
If a function is given wrong type of data,
type error is signaled by the compiler.
4.
Run-time errors(Execution error)
A run-time error is that occurs during the
execution of a program. If it caused of some illegal operation taking place for
the execution of the program. Ex. If an
expression is typing to divide a number by zero is a run time error.
5.
Logical error
A logical error is that error which causes
a program to produce incorrect or undesired output.
Ex. a=7; b=3; c=5;
avg=(a*b*c)/3;
In the above code that is syntactically
correct but will not produce correct output as it has a logical error in it.
Comments
Comments are the pieces of code that the
compiler ignores or simply doesn’t execute. The purpose of comments is only to
allow the programmer to insert some notes to enhance readability or
understand-ability of the program.
There are two ways to insert comment-
1.
Single line comments with //
2.
Multi-line or block comment
with /* */
The cout does not insert line break at the end of the output. endl is a newline character which is used to terminate the line.Same way new line character is '\n'.
This post is about Getting Started with C++ .In the next post we will talk about Data Types, Variables and Constants.
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