Question

C++

So I got this problem http://screencast.com/t/bmZlQ2vCjD

And this is the answer:
http://screencast.com/t/MpX2LqIIB

I dont understand why if (x1 == x2) then cout << "y=" << x1;

That doesn't make any sense mathematically or am I missing something here?

Answer 1

Crap. It HAD to be C++. Well, I can try :p

Answer 2

the only thing I can think of is that it's like that in the 3rd set of plots in the second table.

Answer 3

if `x1 == x2` then it means the slope is `0`

Answer 4

If x1 = x2, then since the x-cordinates are equal, its distance from y axis is constant,
means its the vertical line. and equation of vertical line is of the form y=c
where c = x-coordinate = x1 here

Answer 5

When the slope is `0` you don't want to show the `mx` part.

Answer 6

infinite slope actually.

Answer 7

@ hartnn why nessesarily x1 and not x2 or x ?

Answer 8

you may use x2 also, both x1 and x2 are equal.
so, cout << "y=" << x2;
also works.

Answer 9

Then the code is a bugged, it should be `x = ` not `y = `

Answer 10

and why not y1 - y2 = x too and every other combination with y

Answer 11

oh, yes, it must be cout << "x=" << x1;
and not y=

Answer 12

equation of vertical line is x=x

Answer 13

*x=c

Answer 14

So the solution is wrong?

Answer 15

wio, actually, it shouldn't be x=x1. look at the third set of plots in the second table, and what is says the outcome should be.

Answer 16

that table is incorrect,
x1=x2=-1 implies x=-1

Answer 17

Solution: Kill your teacher.

Answer 18

:D

Answer 19

thats the only flaw, should be cout << "x=" << x1;

Answer 20

so if x1=x2 then the equation of the line is x=x1 ??

Answer 21

@hartnn

Answer 22

Yes....

Answer 23

yes,
x=x1
which is same as x=x2

Answer 24

so this part is wrong too ?
http://screencast.com/t/ePgmeI7jB

Answer 25

if y1=y2, means its horizontal line,
so it must be y=c where c here is y1 or y2
so, yes, thats incorrect.

Answer 26

so we have 2 flaws so far , might even be 3 or 4 -_- I need to dig out the errors that my teacher did -_-

Answer 27

that way, you learn better.

Answer 28

Maybe if we take into consideration the whole if statement, it makes sense?
Like: http://screencast.com/t/syqMgbO9QJ

I can't say that I have mastered C++ either

Answer 29

nah, its just incorrect.
if there are no brackets { and } then only one line condition is assumed, like here.
else , to make a block of instructions as condition, we need curly brackets {...}

Answer 30

Is that incorrect too then http://screencast.com/t/7MGcZlnB6 ?

Answer 31

thats correct,
if m=1, then from y=mx+c
you'll have the equation of the form y=x \(\pm\)c
so the part y=x was displayed first.

Answer 32

`I see, and one last thing,

what about this? http://screencast.com/t/McijZitgnKD

Isn't it stupid to show y = x --c ?

Answer 33

thats not shown
- is displayed first.
then, -c is calculated. , so the second - is for making the 'c' negative and first one is for 'displaying' negative sign.

Answer 34

like if c came out to be -2, then -c = 2
and displayed will be y=mx-2

Answer 35

I mean like, if 3 is calculated with -c it will be -3 right? so we have cout << "-" << -3;

"-" will be - in the message,

so the overall outcome --3?

Answer 36

what 'c' value you have taken ?

Answer 37

if c=3, means c is positive, so it will execute the last else statement,
cout <<"+"<<c
and display +3

if c=-3, then it will execute middle else statement cout<<"-"<<-c {Note : -c=3}\
and displayed will be -3

Answer 38

got it now ?

Answer 39

I see! Thank you!!

Answer 40

welcome ^_^