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Tokens, Expressions and Control Structures

Posted By: Mena Schmidt     Category: C++ Programming     Views: 8708

This article explains about Tokens, Expressions and Control Structures in c++.

Tokens and enums

  • The smallest individual element of a program
  • Keywords, identifiers, constants, strings, ops
  • Few more keywords are added to C++
  • Identifiers have arbitrary length in C++
  • Void *ptr1, char *ptr2 then ptr2= ptr1 is valid in c but not in C++, it is ptr2 = (char *) ptr1
  • Enum not required to precede the declaration
  • Anonymous enums are possible with C++ 
  • enums are not global while defined inside class

Derived Data Types & Symbolic Const

  • Array of strings should be including null char
  • Functions are different in more than one way
  • Char * const ptr = “Good” is allowed in C++ (a constant pointer concept!)
  • Int const *ptr2 = &m is a pointer to a constant where content it points to can not be changed
  • Both of above can be used together
  • C++ requires the const to be initialized ( not 0!)
  • A const is local to a file in C++ (static global in c

Important Differences

  • Strict type checking in C++ to enable FO
  • Anywhere declaration of variable
  • Float k = I/j (Dynamic Initialization) is possible
  • A reference variable like float & sum = total is defined than sum and total are interchangeable
  • A reference variable must be initialized at the time of declaration, init is diff than assignment
  • This is an example of operator overloading
  • It can also be used in funs to return values

Operators in C++

  • The scope resolution operator :: to access a global version of the variable 
  • ::* to declare a pointer to a member of a class
  • ->* to access a member using pointer to the object and a pointer to the member
  • Int *p = new int, float *q = new float, check for !
  • Int *p = new int(25) where 25 is initial value
  • Int *p = new int[25] where 25 is the array size
  • Delete p and delete [<optional size>]p

Manipulators & Type Cast Operator

  • Manipulators are operators used to format disp
  • Cout << “this is testing”<< endl (“\n”)
  • Cout << setw(5) << int1 will display the integer in a space of five chars right justified
  • One can define his/her own manipulators 
  • Function like casting is allowed so sum = j + (float) k can also be written as sum = j + float(k)
  • P = int *(q) is illegal but p = (int *) q or typedef int * int_pt and p = int_pt(q) is legal

-  Mixed data in expression is subject to automatic conversion
-  Integral widening conversion is converting a char or short int to int
-  Operator gets new meaning after being overloaded but do not loose their old meaning
-  Operators have precedence which is not changed
-  All control structures, if, if-else, switch, while, do-while, for loop, work the same way

  
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Mena Schmidt
Mena Schmidt author of Tokens, Expressions and Control Structures is from Frankfurt, Germany.
 
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