Question

该程序假设运行并打印出表面区域，卫星数量和距离太阳的距离。我无法弄清楚如何让定义的数字在程序中工作。任何提示都会有帮助。感谢

#include <stdio.h>
#include <stdlib.h>
#define Mercury_diameter 4879
#define Venus_diameter 12104
#define Earth_diameter 12756
#define Mars_diameter 6792
#define Mercury_distance 57.9
#define Venus_distance 108.2
#define Earth_distance 149.6
#define Mars_distance 227.9
#define Mercury_moons 0
#define Venus_moons 0
#define Earth_moons 1
#define Mars_moons 2
#define PI 3.1415926535

int main()
{

char planet;
printf("Please enter the first letter of the planet whose information you'd        like to see.\n");
printf("Use lower-case letters. Use 'a' for Mars Please! \n");
scanf("%c", &planet);

float m_rad = Mercury_diameter/2.;
float v_rad = Venus_diameter/2.;
float e_rad = Earth_diameter/2.;
float a_rad = Mars_diameter/2.;


float m_surf = 4 * PI * m_rad * m_rad;
float v_surf = 4 * PI * v_rad * v_rad;
float e_surf = 4 * PI * e_rad * e_rad;
float a_surf = 4 * PI * a_rad * a_rad;


switch (planet)
{
   case 'm':
m_surf = 4. * PI * m_rad * m_rad;
printf("The surface area of Mercury = %f \n", m_surf);
printf("Mercury has Mercury_moons moons. \n");
printf("The distance between Mercury and the sun is Mercury_distance \n");
break;

  case 'v':
v_surf = 4. * PI * v_rad * v_rad;
printf("The surface area of Venus = %f \n", v_surf);
printf("Venus has Venus_moons moons. \n");
printf("The distance between Venus and the Sun is Venus_distance \n");
break;

  case'e':
e_surf = 4. * PI * e_rad * e_rad;
printf("The surface area of Earth = %f \n", e_surf);
printf("Earth has Earth_moons moons. \n");
printf("The distance between Earth and the Sun is Earth_distance \n");
break;

  case 'a':
a_surf = 4. * PI * a_rad * a_rad;
printf("The surface area of Mars = %f \n", a_surf);
printf("Mars has Mars_moons moons. \n");
printf("The distance between Mars and the Sun is Mars_distance \n");
break;

  default:
printf("You have entered an invalid entry!");

}

return 0;
}

Answer 1

问题是#defines不会在字符串中被替换。尝试为卫星做这样的事情：

printf("Mars has %d moons. \n", Mars_moons);

Answer 2

宏不会在字符串内扩展。你可以这样做 - 写

printf("The distance between Mercury and the sun is %f\n",Mercury_distance);

另请注意这个问题How to use macros in printf function。

无法获得定义的数字

2 个答案: