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| author | Tobias Klauser <tklauser@distanz.ch> | 2008-01-27 11:37:44 +0100 |
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| committer | Tobias Klauser <tklauser@xenon.tklauser.home> | 2008-01-27 11:37:44 +0100 |
| commit | 7e0f021a9aec35fd8e6725e87e3313b101d26f5e (patch) | |
| tree | b1cacc4b24393f517aeb4610e9e1021f954307a8 /reference/C/CONCEPT/arrays.html | |
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diff --git a/reference/C/CONCEPT/arrays.html b/reference/C/CONCEPT/arrays.html new file mode 100644 index 0000000..b56def1 --- /dev/null +++ b/reference/C/CONCEPT/arrays.html @@ -0,0 +1,212 @@ +<title>Arrays</title> +<body bgcolor="#ffffcc"> +<hr> +<center> +<h1>Arrays.</h1> +</center> +<hr> +Arrays can be created from any of the C data types +<a href="data_types.html#int">int</a>, +<a href="data_types.html#float">float</a>, +<a href="data_types.html#char">char</a>. I start with <b>int</b> and +<b>float</b> +as these are the easiest to understand. Then move onto <b>int</b> +and <b>float</b> +multi dimentional arrays and finally <b>char</b> arrays +<ul> +<li><a href=#int><b>int</b> or <b>float</b> arrays.</a> +<li><a href=#twod>two dimensional <b>int</b> or <b>float</b> arrays.</a> +<li><a href=#char><b>char</b> arrays.</a> +<li><a href=#chard><b>char</b> multidimentional arrays.</a> +</ul> + +<a name="int"> +<hr> +<h2>int and float arrays</h2> +To <a href="../glossary.html#definition">define</a> an integer or +floating point variable you would say. +<pre> + main() + { + int Count; /* integer variable */ + float Miles; /* floating point variable */ + } +</pre> +The syntax for an array is: +<pre> + main() + { + int Count[5]; /* 5 element integer array */ + float Miles[10]; /* 10 element floating point array */ + } +</pre> + +Now, the <b>important</b> fact is that the elements start at 0 (ZERO), so, +'Count' above has elements 0, 1, 2, 3, 4. <p> +To change the value of the 5th element we would code: +<pre> + main() + { + int Count[5]; + Count[4] = 20; /* code 4 to update the 5th element */ + } +</pre> + +If we want to initalise 'Count' at <A HREF="../glossary.html#definition">definition</A> we can say: +<pre> + main() + { + int i; + int Count[5]={10, 20, 30}; + for (i=0; i< 5; i++) + { + printf("%d ", Count[i]); + } + puts(""); + } +</pre> + +The result will be: +<pre> + 10 20 30 0 0 +</pre> +We can see from the example above that the elements that have NOT been +initalised +have been set to zero.<p> +One last thing to show you. If all the elements are being +initialized when the variable is being defined, the compiler can work out +the number of elements for you. So this example will create an array +with 3 elements. +<pre> + main() + { + int i; + int Count[]={10, 20, 30}; + } +</pre> + +Don't forget, all the stuff so far also applies to <b>float</b>. +<p> + +<a name="twod"> +<hr> +<h2>Two dimensional <b>int</b> and <b>float</b> arrays.</h2> + +C does not actually support multi-dimensional arrays, but you can +emulate them. +<pre> + main() + { + int Count[5]; + int Matrix[10][4]; + } +</pre> +<b>Count</b> has been seen before, it defines an array of 5 elements.<p> +<b>Matrix</b> is defined as 10 arrays, all with 4 elements.<p> +To initalise <b>Matrix</b> at definition, you would code the following. +<pre> + main() + { + int Matrix[4][2]={{1, 2}, + {3, 4}, + {5, 6}, + {7, 8}}; + } +</pre> +Dont forget the last element will be <b>Matrix[3][1]</b> +<p> + +<a name="char"> +<hr> +<h2>char arrays.</h2> + +<b>char</b> arrays work in the same way as <b>int</b> and <b>float</b> +<pre> + main() + { + char Letter; + char Letters[10]; + } +</pre> +'Letter' can only hold one character but 'the 'Letters' array could hold 10. +It is important to think of 'char' as an array and NOT a string.<p> +To initalise 'char' variables you can use the following syntax. +<pre> + main() + { + char Letter='x'; + char Letters[10]='f','a','x',' ','m','o','d','e','m','\0'; + char Text[10]="fax modem"; + } +</pre> +Note that the double quotes mean 'text string' and so they will add the +<a href=../SYNTAX/null.html>NULL</a> +automatically. This is the only time that text can be loaded into an array +in this way. If you want to change the contents of the array you should use +the function <a href=../FUNCTIONS/strcpy.html>strcpy</a>. +<p> + +<a name="chard"> +<hr> +<h2>Two dimensional char arrays.</h2> + +Two dimensional arrays are a different kettle of fish! We can follow the +rules above to define the array like this. +<pre> + main() + { + char Colours[3][6]={"red","green","blue"}; + + printf ("%c \n", Colours[0][0]); /* O/P 'r' */ + printf ("%s \n", Colours[1]); /* O/P 'green' */ + } +</pre> + +The example above has reserved 18 consecutive bytes and created three +pointers into them. +<pre> + + --------------------- + |red \0green\0blue \0| + --------------------- + A A A + | | | + Colours[0] ---- | | + Colours[1] ----------- | + Colours[2] ------------------ + +</pre> +<center> +<p> +<font size= +2> +<a href=pointers.html>click here</a> for chat on pointers. +</font> +</center> +<p> +<hr> +<p> +<center> +<table border=2 width=80% bgcolor=ivory> +<tr align=center> +<td width=25%> +<a href="../cref.html">Top</a> +</td><td width=25%> +<a href="../master_index.html">Master Index</a> +</td><td width=25%> +<a href="../SYNTAX/keywords.html">Keywords</a> +</td><td width=25%> +<a href="../FUNCTIONS/funcref.htm">Functions</a> +</td> +</tr> +</table> +</center> +<p> + +<hr> +<address>Martin Leslie +<script language="JavaScript"> +<!-- // +document.write(document.lastModified); +// --> +</script> +</address> |