C++ 浮点/双比较在太阳系模拟中不起作用

我正在用SDL2做一个简单的太阳系游戏/模拟（只有太阳、地球和月亮）。我用一个浮点来表示地球相对于太阳的度数（即0度为东方，90度为向下，等等）。当我尝试将值锁定在0和360之间时，它不起作用

我目前将模拟速度限制为90 fps，并希望每60秒旋转1圈

// The desired FPS and the number of milliseconds (ticks) between frame draws.
const int FPS = 90;
const int TICKS_PER_FRAME = 1000 / FPS;
// The number of seconds it will take for Earth to make one revolution around the sun.
const int EARTH_REVOLUTION_IN_SECONDS = 1 * 60;
// Number of degrees per millisecond for the Earth.
const float EARTH_DEGREES_PER_MILLISECOND = (float)EARTH_REVOLUTION_IN_SECONDS / 360000.0f;

我把地球放在离太阳约1/3电脑屏幕高度的地方，在0.0度时启动地球，然后启动计时器

   // The distance from the Sun's center to the Earth's center. This will be 
   // a quarter of the screen height (presumed to be the smaller dimension).
   int distSunToEarth = resolution_y * 0.3;

   // Starting degrees of Earth relative to the Sun. 0.0 degrees is East.
   float earthDegrees = 0.0f;

   // Amount of time between now and the last frame draw.
   Uint32 deltaTime = 0;
   // The start time. No frames have been drawn yet.
   Uint32 startedTime = SDL_GetTicks();
   // Set current time to the started time.
   Uint32 currentTime = startedTime;

在主循环开始时，我检查经过的时间量是否大于帧之间的时间量

   // Get the current time in milliseconds.
   currentTime = SDL_GetTicks();
   // Calculate how much time has passed since the last frame draw.
   deltaTime = currentTime - startedTime;

   // If the amount of time that has passed is greater than our desired
   // delay between frames, draw the next frame.
   if (deltaTime > TICKS_PER_FRAME) {
      /* Draw Frame */
   }

这是绘制和移动地球的逻辑。地球度数应该保持在0到360之间，但事实并非如此。但是，代码仍然报告它在这些值内

   /* Earth */

   // Determine the center of the Earth. Start from the Sun's center and calculate the
   // x and y values relative to it using Soh-Cah-Toa (Yay, trigonometry!). The degrees must
   // be converted to radians using <degrees> * PI / 180.
   int earthCenterX = backgroundCenterX + (distSunToEarth * cos(earthDegrees * M_PI / 180));
   int earthCenterY = backgroundCenterY + (distSunToEarth * sin(earthDegrees * M_PI / 180));

   // Determine the x and y values needed to center the Earth sprite at the above coordinates.
   int earthSpriteX = earthCenterX - (earthSpriteSheet.GetClipWidth() / 2);
   int earthSpriteY = earthCenterY - (earthSpriteSheet.GetClipHeight() / 2);

   // Render the next frame.
   earthSpriteSheet.RenderNextFrame(earthSpriteX, earthSpriteY);

   // Move the Earth aroudn the Sun. Multiply the number of milliseconds that 
   // have passed by the number of degrees the Earth moves per millisecond.
   earthDegrees += ((float)deltaTime * EARTH_DEGREES_PER_MILLISECOND);

   //printf("degrees: %f.\n", (float)deltaTime * EARTH_DEGREES_PER_MILLISECOND);
   //printf("earthDegrees: %f.\n\n", earthDegrees);

   // If the degrees become negative, loop back to 360.
   //
   // e.g. if earthDegrees become -2.5 degrees, the new degrees would be:
   // 360 deg - abs(-2.5 deg) => 357.5 deg.
   if (earthDegrees < 0.0)
   {
       printf("Less than 0.0");
       earthDegrees = 360.0f - abs(earthDegrees);
   }
   // Else if the Earth becomes greater than 2PI, round back to 0.
   //
   // e.g. if degrees become 362.5, the new degrees would be:
   // 362.5 deg - 360 deg => 2.5 deg.
   else if (earthDegrees > 360.0f)
   {
       printf("Greater than 360.0");
       earthDegrees = earthDegrees - 360.0;
   }
   else if (earthDegrees >= 0.0f && earthDegrees <= 360.0f)
   {
       printf("Between 0 and 360\n");
   }

   printf("earthDegrees: %d.\n", earthDegrees);



   /* 
   ...
   Render code 
   ...
   */

   // Reset the started time and current time to now.
   startedTime = SDL_GetTicks();
   currentTime = startedTime;
   // Reset the change in time to 0.
   deltaTime = 0;

/*地球*/
//确定地球的中心。从太阳中心开始，计算
//使用Soh-Cah-Toa（耶，三角学！）相对于它的x和y值。学位必须
//可以使用*PI/180转换为弧度。
int earthCenterX=backgroundCenterX+（distSunToEarth*cos（earthDegrees*M_PI/180））；
int earthCenterY=backgroundCenterY+（distSunToEarth*sin（earthDegrees*M_PI/180））；
//确定将地球精灵置于上述坐标中心所需的x和y值。
int earthSpriteX=earthCenterX-（earthSpriteSheet.GetClipWidth（）/2）；
int earthSpriteY=earthCenterY-（earthSpriteSheet.GetClipHeight（）/2）；
//渲染下一帧。
earthSpriteSheet.RenderNextFrame（earthSpriteX，earthSpriteY）；
//使地球绕着太阳转。乘以所需的毫秒数
//已经超过了地球每毫秒移动的度数。
earthDegrees+=（（浮点）deltaTime*地球度数/u毫秒）；
//printf（“度数：%f.\n”，（浮点）增量时间*地球度数/u毫秒）；
//printf（“地球度数：%f.\n\n”，地球度数）；
//如果度变为负，则循环回360度。
//
//例如，如果地球度数变为-2.5度，则新度数将为：
//360度-abs（-2.5度）=>357.5度。
如果（地球度<0.0）
{
printf（“小于0.0”）；
地球度=360.0f-绝对值（地球度）；
}
//否则，如果地球变得大于2PI，则返回0。
//
//例如，如果度数变为362.5，则新度数将为：
//362.5度-360度=>2.5度。
否则，如果（地球度>360.0f）
{
printf（“大于360.0”）；
地球度=地球度-360.0；
}
否则，如果（earthDegrees>=0.0f&&earthDegrees
printf（“earthDegrees:%d.\n”，earthDegrees）；
不打印
float
则打印整数

尝试打印（“地球度数：%f.\n”，地球度数）

这似乎是问题所在…我的地球精灵没有移动，但至少度数明显在变化。谢谢。这真的回答了问题吗？发布的问题听起来不像是输出格式问题。另外，使用不正确的格式说明符进行打印是未定义的行为。最好使用

std：：cout

这样你就不会陷入麻烦。