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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.
Variables and pointers and references - C and C++

If I have a variable called "weight" that contains a float, I can use and set its value by using that name.

Pointers

If - in C or in C++ - I declare a variable to be a pointer then that variable may contain a memory address ... I use a * in my type declaration, and then I use & in my assignment:
float * pweight = &weight;

I can then say that I want to use the contents of that variable by preceeeding the name with * in my code, for example:
cout << "www " << *pweight << endl;

References

In C++ only, I can also declare a variable to be a reference by using an & in my declaration:
float & rweight = weight;

A reference gives a variable a second name, and once it has been assigned the variable can be directly accessed by that new name without any extra characters, for example:
cout << "xxx " << rweight << endl ;

References are a commonly used and useful way of giving a variable a second and temporary name without the undue complexity that's imposed by pointers. There are, however, times that you can't do without pointers!

Here's an example of a complete demonstration program:

#include <iostream>
using namespace std;
int main () {
  float weight = 16.8;
/* Pointer */
  float * pweight = &weight;
  cout << "www " << *pweight << endl;
/* Reference */
  float & rweight = weight;
  cout << "xxx " << rweight << endl ;
/* Direct Access */
  cout << "yyy " << weight << endl ;
/* Each of these alters the same variable */
  rweight = rweight + 14.7;
  weight = weight + 3.75;
  *pweight = *pweight + 4.9;
  cout << "zzz " << weight << endl ;
}


Note, specially, how the final three assignments all add to the same variable, but it's referenced in three different ways ... calculating 16.8 + 14.7 + 3.75 + 4.9 when all added together comes to 40.15:

[trainee@easterton lp]$ ./prd
www 16.8
xxx 16.8
yyy 16.8
zzz 40.15
[trainee@easterton lp]$

(written 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)
  [2004] Variable Scope in C++ - (2009-01-22)
  [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)
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  [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)

C207 - C and C based languages - Pointers and references
  [1155] Pointers in C - (2007-04-19)
  [1478] Some new C programming examples - files, structs, unions etc - (2007-12-19)
  [1497] Training Season Starts again! - (2008-01-07)
  [2572] The what and why of C pointers - (2010-01-13)
  [2670] Pointers to Pointers to Pointers - what is the point? - (2010-03-10)
  [3004] Increment operators for counting - Perl, PHP, C and others - (2010-10-18)
  [3121] New year, new C Course - (2011-01-05)
  [3242] How to return 2 values from a function (C++ and C) - more uses of pointers - (2011-04-10)
  [3386] Adding the pieces together to make a complete language - C - (2011-08-11)
  [3399] From fish, loaves and apples to money, plastic cards and BACS (Perl references explained) - (2011-08-20)
  [4128] Allocating memory dynamically in a static language like C - (2013-06-30)
  [4560] Variables, Pointers and References - C and C++ - (2015-10-29)

C201 - C and C based languages - C Language Fundamentals
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  [1671] Compiling C programs with gcc - an overview - (2008-06-10)
  [2842] Staring a C course with Hello World - why? - (2010-06-30)
  [3120] Learning to write good programs in C and C++ - separating out repeated code - (2011-01-04)
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  [4555] Preprocessor directives in C and C++ - what they mean - (2015-10-27)
  [4566] C - why is slow to write and debug) but fast to run? - (2015-11-01)


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