12.I did it,though


#1


https://www.codecademy.com/courses/web-beginner-en-JwhI1/2/4?curriculum_id=50a3fad8c7a770b5fd0007a1


Hey guys. So i wasn't introduced to "parseInt()" and I really wonder if I am going to be introduced to it...or I could use some helpful links to learn about it... w3 did'nt do well explaining its usage...Thanks))


$(document).ready(function() {
    $(document).keydown(function(key) {
        switch(parseInt(key.which,10)) {
			// Left arrow key pressed
			case 37:
				$('img').animate({left: "-=10px"}, 'fast');
				break;
			// Up Arrow Pressed
			case 38:
				$('img').animate({top: "-=10px"}, 'fast'); 
				break;
			// Right Arrow Pressed
			case 39:
				$('img').animate({left: "+=10px"}, 'fast');
				break;
			// Down Arrow Pressed
			case 40:
				$('img').animate({top: "+=10px"}, 'fast');
				break;
		}
	});
});


#2

parseInt() takes a number of any base and converts it to a decimal integer. We can also convert numbers in the form of a string though the Unary operator can fill in for this role.

 > a = +"42"
=> 42
 > a
=> 42
 > typeof a
=> 'number'

   b = "42"
=> '42'
   parseInt(b)
=> 42
   typeof b
=> 'string'
   b = parseInt(b)
=> 42
   typeof b
=> 'number'

That's the basic function. Now lets look at numbers of different bases...

The common bases are binary, octal and hexadecimal, base 2, 8 and 16 respectively. We can pass either number or string, but the results may vary so some practice will help to demonstrate the differences.

parseInt(0b1000, 2)       // NaN

parseInt('0b1000', 2)     // 8

parseInt(1000, 2)         // 8

parseInt(01234, 8)        // 54  ???

parseInt(1234, 8)         // 668

parseInt("01234", 8)      // 668

parseInt(2A, 16)  // SyntaxError: identifier starts immediately after numeric literal

parseInt(0x2A, 16)        // 66    ???

parseInt('0x2A', 16)      // 42

parseInt('2A', 16)        // 42

The output of parseInt() is always a decimal integer. The second argument is the Radix, which specifies the base of the value being passed to the function.


#3

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