Given an angle and length, how do I calculate the coordinates

Question

Assuming the upper left corner is (0,0) and I'm given an angle of 30 degrees, a starting point of (0,300), a line length of 600, how do I calculate the ending point of the line so that the line is representative of the angle given.

The C pseudo-code is

main() {
  int x,y;

  getEndPoint(30, 600, 0, 300, &x, &y);
  printf("end x=%d, end y=%d", x, y);
}

// input angle can be from 0 - 90 degrees

void getEndPoint(int angle, int len, int start_x, int start_y, int *end_x, int *end_y) 
{

    calculate the endpoint here for angle and length

    *end_x = calculated_end_x;
    *end_y = calculated_end_y;
}

Answer 1

math.h has all the trigonometric functions you should need. You may need to give -lm to your linker, depending on what system you're building on (sometimes it's automatic).

Answer 2

// edit to add conversion
    #define radian2degree(a) (a * 57.295779513082)
    #define degree2radian(a) (a * 0.017453292519)

        x = start_x + len * cos(angle);
        y = start_y + len * sin(angle);

Answer 3

Is it the maths or the code you are having trouble with? If it is the maths, then this is probably not the forum, and it is pretty elementary; I refer you to Polar -Rectangular Conversion. Remember however that when you implement it the C math library uses radians rather than degrees r = d * PI / 180.0

Answer 4

You don't say what the angle is measured relative to, or indeed what direction your axes go. These will make a difference.

You first need to convert from degrees to radians (multiply by PI and divide by 180). Then you need to take the sine and the cosine of your angle and multiply these by the length of the line. You now have two numbers for your coordinates, but it depends what directions your axes go and from where you're measuring your angles which of these values is the x coordinate and which is the y, and whether either of them needs to be negated.