学生成绩管理系统输出错误

#include<iostream>
#include<string>
using namespace std;

struct xuesheng
{
    char xingming[30],xingbie[10];
    int chengji[20];
};
void shuru(xuesheng *s,string km[],const int renshu,const int keshu)
{
    for (int i = 0;i<renshu;i++,s++)
    {
        cout << "请输入第" << i + 1 << "个学生的信息" << endl;
        cout << "请输入学生姓名:";
        cin >> s[i].xingming;
        cout << "请输入学生性别:";
        cin >> s[i].xingbie;
        for (int j = 0; j <keshu; j++)
        {
            cout << "请输入学生的"<<km[j]<<"成绩";
            cin >> s[i].chengji[j];
        }
        cout << "第" << i + 1 << "个学生的信息输入完成" << endl;
    }
    cout << "输入结束" << endl;
}
void dankepaixv(xuesheng st[],string km[],const int renshu,const int keshu)
{
    xuesheng itemp;
    for(int i=0;i<keshu;i++)
    {
        for(int j=0;j<renshu-1;j++)
            for(int k=j+1;k<renshu;k++)
                if(st[k].chengji[i]<st[j].chengji[i])
                {
                    itemp = st[j];
                    st[j] = st[k];
                    st[k] = itemp;
                }
        cout<<endl<<km[i]<<":"<<endl;        //输出该科排好的成绩单
        for(int m=0;m<renshu;m++)
            cout<<st[m].xingming<<"        "<<st[m].chengji[i]<<endl;
    }
}
void pingjun(xuesheng st[],string km[],const int renshu,const int keshu)
{
    int s[renshu],x;
    for(int i=0;i<renshu;i++)
    {
        x=0;
        for(int j=0;j<keshu;j++)
            x+=st[i].chengji[j];
        s[i]=x/keshu;
        cout<<st[i].xingming<<"        "<<s[i]<<endl;
    }
}

int main()
{
    //输入
    int r,k;
    cout << "请输入学生人数";
    cin >> r;
    cout << "请输入科目数";
    cin >> k;
    const int renshu = r;
    const int keshu = k;
    string km[keshu];
    for(int i=0;i<keshu;i++)
    {
        cout << "请输入科目名称"<<i+1<<endl;
        cin>>km[i];
    }
    xuesheng s[renshu];
    shuru(s,km,renshu,keshu);



    //主菜单
    while(true)
    {cout << "如果您需要查询单科成绩，请输入\"dk\"；如果您需要查询平均成绩，请输入\"pj\""<< endl;
    cout << "按\"z\"返回主菜单，按\"q\"退出程序" << endl;
    string xuanxiang;
    cin >> xuanxiang;
    if (xuanxiang == "q")
        break;
    else if (xuanxiang =="z")
        continue;
    else if (xuanxiang =="dk")
        dankepaixv(s,km,renshu,keshu);
    else if (xuanxiang =="pj")
        pingjun(s,km,renshu,keshu);
    else
        cout << "输入错误，返回主菜单" << endl;
    }
    return 0;
}