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For 2021 - online Python 3 training - see ((here)).

Our plans were to retire in summer 2020 and see the world, but Coronavirus has lead us into a lot of lockdown programming in Python 3 and PHP 7.
We can now offer tailored online training - small groups, real tutors - works really well for groups of 4 to 14 delegates. Anywhere in the world; course language English.

Please ask about private 'maintenance' training for Python 2, Tcl, Perl, PHP, Lua, etc.
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)


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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.

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