Thread: Math function deg/rad query

I've gone and got myself confused with this little program It's meant to find the height of a triangle in degrees, when the angle of elevation (y) and the distance accross (x) is known, and output it in some sort of table (formatting, however, is not important at this stage.) It does this, but of course only in Radians.

I put the chunk of code following "float height....." in to convert to degrees, but it seems to do nothing. Even when I change the values, it has no effect on the program.

Here's the code I have, and note, this is a UK keyboard setup, so I couldn't work out the "hash" symbol. For the sake of this, I'll just write hash. How can I make this thing output Degrees instead of Radians?

Code:

hash include <cstdlib>
hash include <iostream>
hash include <iomanip>
hash include <math.h>

using namespace std;

float height (float x, float y)
{return x*(180/3.141593);
return y*(180/3.141593);
}

int main()
{ for (float x=0; x <=60; x+=10)
{ for (float y=0; y <=85; y+=5)
cout << setw(12) << (tan(y)*x);
cout << endl;
}
}

Thanks,
George

First, you can't return multiple values in c/c++. For this, you need to use pointers in C.
Second, You need to actually call the function that does the conversion.

Originally Posted by GeorgeV

Here's the code I have, and note, this is a UK keyboard setup, so I couldn't work out the "hash" symbol.

The hash key is next to the return key in the middle row on a standard UK keyboard

Code:

float height (float x, float y)
{return x*(180/3.141593);
return y*(180/3.141593);
}

As nempo said, you can't return multiple values from a function, although since you're using C++, don't use pointers, use references, which will allow you to directly modify the values in-situ. eg,

Code:

void height (float & x, float & y)
{
    x = x *(180/3.141593);
    y = y *(180/3.141593);
}

you could also investigate the struct keyword which will allow you to create your own type to combine X and Y together.

Code:

struct coordinate
{
    double x, y;
};

/* ... */

coordinate to_degrees( double x, double y )
{
    coordinate coo;
    coo.x = x *(180/3.141593);
    coo.y = y *(180/3.141593);
    return coo;
}

(By the way, I reccommend using double's instead of float's - the double type has a much greater precision. the typical precision of float is around 6 significant figures on most modern desktops)

1) As Bench82 suggested, use doubles.
2) Instead of a function that converts two arguments simultaneously, consider a function that converts a single argument, and calling it twice. Then you don't need pointers or references at all, you can use the regular return value. Also, by using the inline keyword, assuming the compiler takes the hint, the function call gets reduced to a single multiplication and there's no more overhead than calling a two-argument function once.
3) Consider expressing pi symbolically.

Code:

#include <cmath>

const double Pi = 4.*std::atan(1.);

(among other possible expressions for pi).

Thanks everybody for all the tips!

Re the "hash" key: I can't find it on this keyboard. It's pictured on the '3' key, but this only gives the '£' sign when combined with 'Shift'.

Next to the return key you say, Bench82? Unfortunately I'm just not seeing it. (Of course, I won't be programming on this laptop.)

As someone pointed out, floats offer enough precision for this task, but I've switched to doubles anyway.

and people say no one uses trigraphs anymore.

Code:

	

		

			

			
				5.2.1.1 Trigraph sequences
1 All occurrences in a source file of the following sequences of three characters (called
trigraph sequences12)) are replaced with the corresponding single character.
??= #
??( [
??/ \
??) ]
??' ^
??< {
??! |
??> }
??- ~
No other trigraph sequences exist. Each ? that does not begin one of the trigraphs listed
above is not changed.
2 EXAMPLE The following source line
printf("Eh???/n");
becomes (after replacement of the trigraph sequence ??/)
printf("Eh?\n");
			
		
	

code block to appease cboard server.

Originally Posted by robatino

I starting programming in C in 1990 and have never used trigraphs, since every keyboard I've used even back then had all the basic characters. I only know about them from K&R2.

I was speaking in absolutist terms.

#define isn't recommended, use const type var = value;

For something as simple as this it's just fine.

Originally Posted by GeorgeV

Next to the return key you say, Bench82? Unfortunately I'm just not seeing it. (Of course, I won't be programming on this laptop.)

In that case your laptop has an American keyboard, but windows is treating it like a UK one.

Again, thanks for the help. I'm now using <cmath> instead, and at the moment I'm also using references. So this bit reads something like so:

Code:

void height (float & x, float & y)
{
    x = x *(180/M_PI);
    y = y *(180/M_PI);
}

But I'm having trouble calling the 'height' function properly. What is the correct syntax I should be using?