"unsafe use of type 'bool' in operation"

"unsafe use of type 'bool' in operation"
我的程序是
#include
using namespace std;
void main()
{
char c1='a',c2='b',c3='c';
int i1=10,i2=20,i3=30;
double d1=0.1,d2=0.2,d3=0.3;
double x;
x=i1>i2>i3