js: loops and selection, arrays and random
jbwyatt.com
Tryit Editor
1. LOOP and show (alert) the five numbers , 0-4 using "for"
<script type="text/javascript">
var i;
for( i=0; i<5; i++)
{
alert(i);
}
</script>
2. LOOP with IF using "while" and "do while"
<script type="text/javascript">
//LOOP through the numbers 0-9, showing (alert) IF even #s using "while"
var i=0;
while( i < 10)
{
if(i % 2 === 0)
alert(i);
i++;
}
// LOOP through the numbers 1-10, showing IF odd #s using "do while"
var i=1;
do{
if(i % 2 === 1)
alert(i);
i++;
}while( i <= 10);
</script>
3. ARRAY
<script type="text/javascript">
var i;
// declare an array called billy with 5 items
// index of items is 0 thru 4
var billy = new Array(5);
// fill array with numbers 0, 2, 4, 6, 8
for(i=0; i < billy.length; i++)
billy[i] = i * 2;
// write out array as a series of header level 6
for(i=0; i < billy.length; i++)
document.write("<h6>" + billy[i] +"</h6>)";
// now fill array with 10, 15, 20, 25, 30 - see the trick?!!
billy[0] = 10;
for(i=1; i < billy.length; i++)
billy[i] = billy[i-1] + 5; // adds 5 to the PREVIOUS ELEMENT in the array
</script>
<script type="text/javascript">
var i;
// declare an array called billy with 5 items
// index of items is 0 thru 4
var billy = new Array(5);
// fill array with numbers 0, 2, 4, 6, 8
for(i=0; i < billy.length; i++)
billy[i] = i * 2;
// write out array as a series of header level 6
for(i=0; i < billy.length; i++)
document.write("<h6>" + billy[i] +"</h6>)";
// now fill array with 10, 15, 20, 25, 30 - see the trick?!!
billy[0] = 10;
for(i=1; i < billy.length; i++)
billy[i] = billy[i-1] + 5; // adds 5 to the PREVIOUS ELEMENT in the array
</script>
4. LOOP through numbers 0-99, put the numbers in an ARRAY and print with document.write()
<script type="text/javascript">
// variable used as an index
var i=0;
// declare an array - indexes go from 0-99
// name of the array is "list"
var list = new Array(100);
// loop thru numbers 0-99, double the number and put that number an array slot
// [0][2][4][6] ... [196][198]
do
{
list[i] = i*2; // put the number INTO the array
i++;
}while( i <= 100 );
// print out first 5 numbers in array
for (i=0; i< 5; i++)
document.write(list[i] + " ");
document.write("<br />");
// print out last 5 numbers in array
for (i=95; i< 100; i++)
document.write(list[i] + " ");
document.write("<br />");
</script>
5. PROMPT & fill an ARRAY with RANDOM numbers and print contents in color
<script type="text/javascript">
var size = prompt("Enter the size of the array");
var list = new Array(size);
// fill array
for (i=0; i< size; i++)
list[i] = Math.random(); // number from 0 upto, but not including 1
// print out numbers in array in color
for (i=0; i< size; i++)
document.write("<span style='color:red'>" + list[i] + " <br /></span>");
document.write("<br />");
// fill array again
for (i=0; i< size; i++)
list[i] = Math.random() * 100; // number from 0 upto not including 100
// print out numbers in array in color
for (i=0; i< size; i++)
document.write("<span style='color:red'>" + list[i] + " <br /></span>");
document.write("<br />");
</script>