I'm still develloping my calculator :p

But, there is another problem:

sin(number1);

tan(number1);

do not give the same output as my other calculator (The one which I take to school)!

No error, and I included math.h.

What am I doing wrong?

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- 02-03-2006Ideswatan() and sin()
I'm still develloping my calculator :p

But, there is another problem:

sin(number1);

tan(number1);

do not give the same output as my other calculator (The one which I take to school)!

No error, and I included math.h.

What am I doing wrong? - 02-03-2006Dave_Sinkula
Feeding degrees where radians are expected?

Show an example of expected input and output. - 02-03-2006Salem
math.h functions take parameters measured in radians, not degrees.

There are 2*PI radians in a full circle, scale your angles appropriately. - 02-03-2006Ideswa
sin(1); in computer: 0.841471

sin(1); in school calculator: 0.017452406 - 02-03-2006Cactus_HuggerQuote:

Originally Posted by**Ideswa**

sin(1 degree) = .0174524

sin(1 radian) = .8414709

Radians and degrees are sort of like feet and meters. Just different way of measuring, for the most part. 2 * pi radians = 360 deg, as Salem said, so: pi radians = 180 degrees, pi / 2 radians = 90 deg, etc. Google it. See MathWorld's article on it, or perhaps the Wikipedia entry. - 02-03-2006Ideswa
Thanks!

this is my solution:

tangens = tan(number1);

answer = (2 * M_PI) * tangens;

aswer /= 360;

answer /= tangens;

http://www.functionx.com/bcb/math/PI.htm says:

"....Borland had included its value in the math.h library as M_PI 3.14159265358979323846."

But when I

cout << M_PI;

the output is:

3.14159

And because of that there is still a little difference between the answers:

0.017455064 (in school calc.)

0.0174533 (in my calc.)

Can I change that configuration or is that impossible with a Borland compiler? - 02-03-2006jwenting
cout will use formatting rules for output which concatenate the number.

The Windows calculator will give you .017452406

Which just goes to show that you shouldn't trust default math libraries for extreme precision. - 02-03-2006Rashakil Fol
I'm pretty sure your school calculator's answer of 0.017455064 is off the mark, because I have two calculators that give 1.7452406437, which agrees with the Windows calc. Your calculator's "answer" of 0.0174533 is an approximation of pi/180.

And it looks like that's what you're doing, too.

Code:`answer = (2 * M_PI) * tangens;`

aswer /= 360;

answer /= tangens;

Code:`answer = (2 * M_PI) * tangens / 360 / tangens`

- 02-04-2006Sang-draxQuote:

Originally Posted by**Ideswa**

The reason it almost works is that

tan(1 degree) = tan( pi/180 radians) ~= pi/180.

For small angles (in radians), tan(x)~=sin(x)~=x. This approximation is often used in mechanics.

EDIT: Approximations of tan(1 degree):

Windows calc: 0.017455064928217585765128895219728

MATLAB: 0.01745506492822 - 02-04-2006dwksQuote:

Can I change that configuration or is that impossible with a Borland compiler?

*****and then redefine PI:

Code:`#undef PI`

#define PI 3.1415926535897932384626433832795028841971693993751\

05820974944592307816406286208998628034825342117067\

98214808651328230664709384460955058223172535940812\

84811174502841027019385211055596446229489549303819\

64428810975665933446128475648233786783165271201909\

14564856692346034861045432664821339360726024914127\

37245870066063155881748815209209628292540917153643\

67892590360011330530548820466521384146951941511609\

43305727036575959195309218611738193261179310511854\

80744623799627495673518857527248912279381830119491\

*****You may not have to #undef PI, but I would put it in anyway. - 02-04-2006arjunajay
dwks, but the double can hold only so much.

so even if you gave one million digits the resultant number would be rounded? - 02-04-2006iMalcQuote:

Originally Posted by**dwks**

Just use this:

inline double sin_degrees(double x)

{

return sin(x * (M_PI / 180.0));

} - 02-05-2006grumpy
Technically, M_PI is non-portable. While it's true several compilers (or their libraries) support it, there is no requirement in the C++ standard that it be supported.