一、剔除数字字符

#include<bits/stdc++.h>
using namespace std;
int main()
{
    string s;
    getline(cin,s);
    for(char x : s)
    {
        if(x<'0'||x>'9')
            cout<<x;
    }
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
    string s;
    getline(cin,s);
    int j=0;
    for(int i=0;i<s.size();i++)
    {
        if(s[i]<'0'||s[i]>'9')
            s[j++]=s[i];
    }
    s[j]='\0';
    cout<<s;
    return 0;
}

二、统计各位上等于b的数字数目

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n;
    cin>>n;
    while(n--)
    {
        int a,b;
        cin>>a>>b;
        if(b<0||b>9)
            cout<<"第二个参数越界"<<endl;
        else
        {
            int res=0;
            while(a)
            {
                if(a%10==b)
                    res++;
                a/=10;
            }
            cout<<res<<endl;
        }
    }
    return 0;
}

三、建立一个学生在某一个课程到课情况统计程序

#include<bits/stdc++.h>
using namespace std;
struct Student
{
    string id;
    int normal;
    int late;
    int absence;
    int total;
    double AttendRate;
};
void printStudentRate(Student student) {
    printf("学号：%s, 出勤率：%.2lf\n", student.id.c_str(), student.AttendRate);
}
int main()
{
    int n,totalcourse;
    cin>>n>>totalcourse;
    Student student[n];
    for(int i=0;i<n;i++)
    {
        string id;
        int normal,late,absence;
        cin>>id>>normal>>late>>absence;
        int total=totalcourse; 
        double attendrate=(double)(normal+late)/totalcourse;
        student[i]={id,normal,late,absence,total,attendrate};
    }
    printStudentRate(student[0]);
    for (int i = 0; i < n; i++) {
        cout << "学号：" << student[i].id << ":" << endl;
        cout << "总课时：" << student[i].total << endl;
        cout << "正常：" << student[i].normal << endl;
        cout << "迟到：" << student[i].late << endl;
        cout << "旷课：" << student[i].absence << endl;
        cout << "出勤率：" << student[i].AttendRate << endl;
        double absentRate = (double) student[i].absence / totalcourse;
        cout << "旷课率：" << absentRate << endl;
        puts("---------------------------");
    }
    int normalTotal = 0, lateTotal = 0, absentTotal = 0;
    double attendRateTotal = 0;
    for (int i = 0; i < n; i++) {
        normalTotal += student[i].normal;
        lateTotal += student[i].late;
        absentTotal += student[i].absence;
        attendRateTotal += student[i].AttendRate;
    }
    cout << "总正常次数: " << normalTotal << endl;
    cout << "总迟到次数: " << lateTotal << endl;
    cout << "总旷课次数: " << absentTotal << endl;
    cout << "平均出勤率: " << attendRateTotal / n << endl;
}