#include "stdio.h"
void main()
{double a,b,c;  
double maxY =20;              
     b =18.98;      
     c =1.02;      
     a=maxY-b;     //即maxY-b=1.02
   
    if(a==c)
    {
     printf("与y相切\n");              
    }         
}  

哦，原来是这样。非常谢谢您！