January 23, 2020

Answer to JavaScript Exercise Q2

 

//declare variables
var num, cube;
/* declare and initialise some more variables
and assign the input from two dialogue boxes
*/
var numStr = window.prompt('Enter a number', '');
//convert string variable to number
num = parseFloat(numStr);
// form the cube
cube = num * num * num;
//output a suitable message
document.write('The cube of ' + num + ' is:' + '<BR>');
//convert the cube to a string and output the value
document.write(cube);
//note that you can also write
//document.write(cube.toString());

Notes:

  • All input made via a dialogue prompt box will be in the form of a string. Consequently one needs to be very careful when numbers are being manipulated, in which case explicit conversion will be required by using the parseFloat() function.
  • When passing a value for output, via the browser or an alert box, JavaScript will automatically attempt to convert this value to a string. I have written
    document.write(cube);
    even though cube is a number data type the interpreter will use auto conversion to construct a string. The final alternative
    document.write(cube.toString());
    is in fact not needed because this is what JavaScript does when it applies auto conversion. The number, referenced by cube, is converted to a String object, which is then operated on by the toString() method.

 

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