递增序列的查找
补充：return -1的解释

#include <iostream>
using namespace std;
int s[1000];
int search(int str[],int left,int right,int num){while(left<=right){//要不断循环查找-while:既可判断，又可循环int mid=(left+right)/2;if(num==str[mid])return mid;else if(num<str[mid])right=mid-1;//在左边找else left=mid+1;//在右边找}return -1;//非法区间
}
int main(){int n,num;cin>>n>>num;for(int i=0;i<n;i++)cin>>s[i];cout<<search(s,0,n-1,num)<<endl;return 0;
}

同理递减序列的查找

#include <iostream>
using namespace std;
int s[1000];
int search(int str[],int left,int right,int num){while(left<=right){//要不断循环查找-while:既可判断，又可循环int mid=left+(right-left)/2;//等同(left+right)/2,可避免因left与right过大而溢出的问题if(num==str[mid])return mid;else if(num<str[mid])left=mid+1;//在右边找else right=mid-1;//在左边找}return -1;//非法区间
}
int main(){int n,num;cin>>n>>num;for(int i=0;i<n;i++)cin>>s[i];cout<<search(s,0,n-1,num)<<endl;return 0;
}

如何计算根号数的近似值

#include <cstdio>
#include<cmath>//sqrt
using namespace std;
const double eps=1e-5;
double Func(double n){//求平方的函数，求平方根return n*n;
}
double index(double left,double right){//区间double mid=0.0;while(left-right>eps){mid=(left+right)/2.0;if(Func(mid)>right)//以mid为准，近似数在左端right=mid;else left=mid;}return mid;//相当于left与right
}
int main(){double l,r;scanf("%lf%lf",&l,&r);double y=index(l,r);printf("%.6lf",y);return 0;
}