#include<bits/stdc++.h>
using namespace std;

int main(){
	srand(time(0));
	int r[5]={};
	int a=0,b=0;
	int la;
	long long sum=0;
	for(int i=1;i<=10000000;++i){
		if(rand()%2)continue;
		if(rand()%2)++a;
		else ++b;
	}
	cout<<a<<" "<<b<<endl<<1.0*a/(a+b);
	return 0;
}

0.500632

#include<bits/stdc++.h>
using namespace std;

int main(){
	srand(time(0));
	int r[5]={};
	int a=0,b=0;
	int la;
	long long sum=0;
	for(int i=1;i<=10000000;++i){
		if(rand()%2)++a;
		else ++b;
	}
	cout<<a<<" "<<b<<endl<<1.0*a/(a+b);
	return 0;
}

0.500001

为什么？