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<html>
<head>
<title>Reference variables</title>
</head>
<body bgcolor="#dddddd">
<font color=brown>
<hr>
<center><h1>Reference Variables.</h1></center>
<hr>
<p>
Reference variables allow two variable names to address the
same memory location. The following example shows the
technique in its simplest form.
<p>
<center>
<table border=1 width="80%" bgcolor="ivory">
<tr>
<td>
<pre>
#include <iostream.h>
main()
{
int var1;
int &var2 = var1; // var2 is a reference variable.
var1 = 10;
cout << "var1 = " << var1 << endl;
cout << "var2 = " << var2 << endl;
}
</pre>
</td>
</tr>
</table>
</center>
<p>
Generally, you would not use a reference variable
in this way. Its more likely that they would be used
in function parameter lists to make the passing of
pointers more readable.
<p>
This gives C++ the ability to provide a
different approch to changing a variable from within a
function. Consider the two following programs.
<p>
<center>
<table border=1 width="80%" bgcolor="ivory">
<tr>
<td>
<pre>
#include <stdio.h>
void Square(<b>int *pVal</b>);
main()
{
int Number=10;
printf("Number is %d\n", Number);
Square(<b>&Number</b>);
printf("Number is %d\n", Number);
}
void Square(<b>int *pVal</b>)
{
<b>*pVal</b> *= <b>*pVal;</b>
printf("Number is %d\n", <b>*pVal</b>);
}
</pre>
</td>
<td>
<pre>
#include <stdio.h>
void Square(<b>int &Val</b>);
main()
{
int Number=10;
printf("Number is %d\n", Number);
Square(<b>Number</b>);
printf("Number is %d\n", Number);
}
void Square(<b>int &Val</b>)
{
<b>Val</b> *= <b>Val</b>;
printf("Number is %d\n", <b>Val</b>);
}
</pre>
</td>
</tr>
</table>
</center>
<p>
The program on the right should be clearer to read
because you do not need to worry about pointer
dereferencing.
<hr>
<h2>Examples:</h2>
<img src="../../GRAPHICS/computer.gif" alt="o">
<a href="..//EXAMPLES/refvar.cc">Example program.</a>
<p>
<font color=brown>
<img src="../../GRAPHICS/computer.gif" alt="o">
<a href="../../C/EXAMPLES/pointer_func.c">Example C program.</a>
</font>
<hr>
<h2>See Also:</h2>
</font>
<hr>
<font color=black>
<h2>C References</h2>
<p>
<img src="../../GRAPHICS/whiteball.gif" alt="o">
<a href="../../C/CONCEPT/data_types.html">data types</a>.
</font>
<hr>
<p>
<center>
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<tr align=center>
<td width="25%">
<a href="../cref.html">Top</a>
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</table>
</center>
<p>
<hr>
<font color=brown>
<address>Martin Leslie
29-Sep-96</address><p>
</font>
</body>
</html>
|
