Calculating co-ordinates for a sprite in C++

I am trying to calculate the angle of movement for a sprite in C++.

Although at the moment I am just using the console to output my results.

开发者_JAVA技巧

My problem is that when My results are shown in the console, I cannot get the x axis to go into minus numbers.

Unfortunately I have only just learned about basic trig so I have no idea if I am just doing my maths wrong.

For example: If I choose my angle as 270 and my speed as 1, the console shows the new co-ordinates as (1,-1) when I thought it should be (-1,0)

Equally if I try my angle as -90 and my speed as 1 I get (0,-1)

Is it just that x cannot go into minus numbers?

Or am I making a fundamental mistake?

My code is below - So if anybody could point out what I am doing wrong it would be greatly appreciated.

#include <iostream>
#include <cmath>

using namespace std;

const float PI = 3.14159265;

class sprite {
    public:
        int x;
        int y;
        int angle;
        int speed;
        sprite();
};

sprite::sprite() {
    x = 0;
    y = 0;
    angle = 0;
    speed = 0;
}

int main() {
    int userInput = 0;
    sprite mySprite;

    cout << "Starting co-ordinates: (" << mySprite.x << "," << mySprite.y << ")\n\n";

    while(userInput != 999) {
        cout << "Angle to move: ";
        cin >> userInput;
        mySprite.angle = userInput;

        cout << "Speed to move at: ";
        cin >> userInput;
        mySprite.speed = userInput;

        mySprite.x += ceil(cos(mySprite.angle*PI/180)*mySprite.speed);
        mySprite.y += ceil(sin(mySprite.angle*PI/180)*mySprite.speed);

        cout << "\n\n";
        cout << "New co-ordinates: (" << mySprite.x << "," << mySprite.y << ")\n\n";
    }

    return 0;
}

---

Change to:

    mySprite.x += floor(cos(mySprite.angle*PI/180)*mySprite.speed + 0.5);
    mySprite.y += floor(sin(mySprite.angle*PI/180)*mySprite.speed + 0.5);

And read this (or any other guide you like) to understand why.

---

For a start, the answer you should expect is (0,-1), not (-1,0) (0 is right, 90 is up, 180 is left, 270 is down). The reason you get (1,-1) is because the limitations of floating-point mean that your cos and sin results are (1e-8, -1). You then take the ceil of these, which are (1, -1). You probably want to round rather than take the ceiling.