Home Accessibility Courses Twitter The Mouth Facebook Resources Site Map About Us Contact
 
For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))
Variable Scope in C++

In C++, a variable is 'scoped' to the block in which it is declared. In other words, it exists from the point at which you tell the compiler what type of value it contains through to the close brace at that matches the open brace preceeding that declaration.

In the most frequent use, this means that a variable defined inside a loop doesn't exist after the loop has been exited. And that's very useful indeed in clearing down temporary memory storage for use within the loop's iterations. If you should happen to have another variable of the same name in the outer code (usually a daft thing to do!), its contents will NOT be visible within the inner block as they'll be masked by the more local variable, but they will be unmasked after the outer block is exited.

You can even set up a block that's not a loop and not a conditional - that's there purely to scope variables - if you wish. Simply use a pair of culry braces without any if, while or other keyword. Here's a code example that demsonstrates these features:

#include <iostream>
using namespace std;
 
int main () {
   int demo[12] = {31,28,31,30,31,30,31,31,30,31,30,31};
   int k;
 
   int answer = 42;
 
   for (k=0; k<12; k++) {
 
      int answer = demo[k]; /* masks the original answer */
      cout << answer << ", ";
      }
 
   cout << endl << "hidden was " << answer << endl;
 
   { /* This block is only for scoping purposes */
   float answer = 3.1415;
   cout << answer << " is something to do with cherry pie" ;
   }
 
   cout << endl << "hidden was " << answer << endl; /* the original again */
}


When I run that code, my results look like this:

[trainee@easterton lp]$ ./vscpp
31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31,
hidden was 42
3.1415 is something to do with cherry pie
hidden was 42
[trainee@easterton lp]$

(written 2009-01-22, updated 2009-01-23)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
C234 - C and C based languages - Further C++ Object Oriented features
  [801] Simple polymorphism example - C++ - (2006-07-14)
  [802] undefined reference to typeinfo - C++ error message - (2006-07-15)
  [831] Comparison of Object Oriented Philosophy - Python, Java, C++, Perl - (2006-08-13)
  [1159] It can take more that one plus one to get two. - (2007-04-22)
  [1819] Calling base class constructors - (2008-10-03)
  [2005] Variables and pointers and references - C and C++ - (2009-01-23)
  [2576] What does const mean? C and C++ - (2010-01-15)
  [2673] Multiple Inheritance in C++ - a complete example - (2010-03-12)
  [2717] The Multiple Inheritance Conundrum, interfaces and mixins - (2010-04-11)
  [2849] What are C++ references? Why use them? - (2010-07-02)
  [3057] Lots of things to do with and within a C++ class - (2010-11-16)
  [3069] Strings, Garbage Collection and Variable Scope in C++ - (2010-11-25)
  [3124] C++ - putting the language elements together into a program - (2011-01-08)
  [3238] Bradshaw, Ben and Bill. And some C and C++ pointers and references too. - (2011-04-09)
  [3430] Sigils - the characters on the start of variable names in Perl, Ruby and Fortran - (2011-09-10)
  [3509] Operator Overloading, Exceptions, Pointers, References and Templates in C++ - new examples from our courses - (2011-11-06)
  [3982] Using a vector within an object - C++ - (2013-01-19)
  [4366] Changing what operators do on objects - a comparison across different programming languages - (2014-12-26)
  [4377] Designing a base class and subclasses, and their extension, in C++ - (2015-01-01)
  [4559] When do I use the this keyword in C++? - (2015-10-29)

C231 - C and C based languages - Introduction to C++
  [317] Programming languages - a comparison - (2005-05-20)
  [318] Choosing a theme - (2005-05-20)
  [336] Targetted Advertising - (2005-06-05)
  [928] C++ and Perl - why did they do it THAT way? - (2006-11-16)
  [2169] When should I use OO techniques? - (2009-05-11)
  [2845] Objects and Inheritance in C++ - an easy start - (2010-07-01)
  [3052] Getting your C++ program to run - (2010-11-15)
  [3053] Make - automating the commands for building and installing - (2010-11-16)
  [3250] C++ - how we teach the language and the concepts behind the language - (2011-04-17)
  [4466] Moving from C to C++ - Structured to Object Oriented - a lesson for engineers - (2015-03-28)
  [4561] Hello World in C++ - a first program, with the process explained - (2015-10-30)
  [4562] Left shift operator on an output stream object - C++ - (2015-10-30)


Back to
Discount Training Courses - PHP, Perl, Python
Previous and next
or
Horse's mouth home
Forward to
Variables and pointers and references - C and C++
Some other Articles
The Month Ahead - What is happening in Melksham
Launch of Melksham Food and Drink Festival
Contrast
Variable Scope in C++
Discount Training Courses - PHP, Perl, Python
New C Examples - pointers, realloc, structs and more
I have not programmed before, and need to learn
2000th article - Remember the background and basics
How low can you sink?
4759 posts, page by page
Link to page ... 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96 at 50 posts per page


This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

Link to Ezine home page (for reading).
Link to Blogging home page (to add comments).

You can Add a comment or ranking to this page

© WELL HOUSE CONSULTANTS LTD., 2024: 48 Spa Road • Melksham, Wiltshire • United Kingdom • SN12 7NY
PH: 01144 1225 708225 • EMAIL: info@wellho.net • WEB: http://www.wellho.net • SKYPE: wellho

PAGE: http://www.wellho.net/mouth/2004_Var ... in-C-.html • PAGE BUILT: Sun Oct 11 16:07:41 2020 • BUILD SYSTEM: JelliaJamb