#include <stdio.h>
#include <stdlib.h>
void compare(float,float,float);
float a=80.6,b=24.7; 
int main(void)
{
    float c=77.5;
    compare(a,b,c);                             
    system("pause");
    return 0;
}
void compare(float a, float b, float c)
{
  int temp = 0;
  if ( a < b )
  { temp = b; b = a; a = temp; }
  if ( a < c )
  { temp = c; c = a; a = temp; }
  if ( b < c )
  { temp = c; c = b; b= temp; }
printf("排序后:%.3f %.3f %.3f\n",a,b,c); 
  // 经过上面比较之后结果会由大到小排列
} 

void compare(float a, float b, float c)
{
int temp = 0;  // <--- 因为你说要浮点数这里也要改成float
if ( a < b )
{ temp = b; b = a; a = temp; }
if ( a < c )
{ temp = c; c = a; a = temp; }
if ( b < c )
{ temp = c; c = b; b= temp; }
printf("排序后:%.3f %.3f %.3f\n",a,b,c); 
// 经过上面比较之后结果会由大到小排列
}