C++ 浮点数比大小

// ConsoleApplication1.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>

int _tmain(int argc, _TCHAR* argv[])
{
	//因为-1变成255
	int a = -1;
	unsigned int b = 1;
	if (a > b){
		std::cout << "a >b\n";
	}
	else{
		std::cout << "a <=b\n";
	}

	//
	float c = 0.000003;
	float d = 0.000001;
	printf("%f-%f\n", c, d);
	//这种比较是错的
	if (c > d){
		std::cout << "c ==d\n";
	}
	else{
		std::cout << "c !=d\n";
	}
	//这种比较浮点数的方式是对得	
	if (abs(c - d) > 0.000001){
		std::cout << "c > d\n";
	}
	else{
		std::cout << "c <= d\n";
	}

	getchar();
	return 0;
}

输出结果

a >b
0.000003-0.000001
c ==d
c > d