请问switch里面的为什么第一个case 0要用break，而第二个case不用break

请教switch里面的为什么第一个case 0要用break，而第二个case不用break?

C/C++ code

#include <iostream>#include <stdlib.h>#include <time.h>using namespace std;int main(){    int a,b,numOfQues=0,numOfRight=0;    char inchar;    srand((unsigned int)time(NULL));    cout<<"……欢迎来做两位数的加减法……"<<endl;    do    {        int temp=rand()%2;        a=rand()%100;        b=rand()%100;        switch(temp)        {            case 0:                {                    int ans;                    cout<<a<<'+'<<b<<'=';                    cin>>ans;                    if(a+b==ans){                        numOfRight++;                        cout<<"恭喜您!答对了！"<<endl;                    }else                        cout<<"答错了,再接再厉！"<<endl;                    break;                }            case 1:                {                    int ans;                    cout<<a<<"-"<<b<<"=";                    cin>>ans;                    if(a-b==ans)                    {                        numOfRight++;                        cout<<"恭喜您！回答正确！"<<endl;                    }else                        cout<<"不好意思，回答错误！"<<endl;                }        }        numOfQues++;        cout<<"您还要再做一题吗？（键入N退出）"<<endl;        cin>>inchar;    }while(inchar!='n'&&inchar!='N');    cout<<"您的答案正确率为："<<numOfRight/numOfQues*100/100<<"%.再见！"<<endl;    return 0;}