#include <stdio.h>
 
int main()
{ 
int i, n = 0;
float x = 1, y1 = 2.1 / 1.9, y2 = 1.9 / 2.1;
 
for ( i = 1; i < 22; i++)
x = x * y1;
 
while ( x != 1.0 )
{
x = x * y2; n++;
}
 
printf( "%d\n", n );
 
return 0; 
}

浮点类型不能精确相等