c++程序设计原理与实践 第四章部分答案

#include <iostream>
using namespace std;

int main()
{
    int a=1,b=100;
    int f=1;
    char c=0;

    while(f<=7 && (b-a)>=1)
    {
        cout<<"你的数小等于"<<(a+b)/2<<"吗？(y/n)";
        cin>>c;
        if(c=='n')
            a=(a+b)/2+1;
        else
            b=(a+b)/2;
        f++;
    }
    cout<<(a+b)/2<<endl;
    while (true);
}

#include "../../st.h"

int main()
{
    int sum=0;
    int i=1;
    while(sum<1000)
    {
        int s=1;
        for(int n=1;n<i;n++)
            s*=2;
        sum+=s;
        i++;
    }

    cout<<"it is "<<i-1<<endl;

    while(1);
    return 0;
}

#include "../../st.h"
//要得到自然数n以内的全部素数，必须把不大于的所有素数的倍数剔除，剩下的就是素数。
const int  MAX=101;

int main()
{
    int all[MAX];
    int N,i,j,s;
   // memset(all,1,sizeof(all));
    for(i=0;i<MAX;i++)    //初始化
        all[i]=1;

    for(i=2;i<MAX;i++)     //倍数关系
        if(all[i])
            for(j=i+i;j<=MAX;j+=i)
                all[j]=0;
    while(cin>>N)
    {
        for(i=2;i<=N;i++)
            if(all[i])
                cout<<i<<"  ";
        cout<<endl;
    }
    return 0;
}

#include "../../st.h"
//学到后面这些都是小case= =
int main()
{
    vector<int> all;
    vector<int>    s;
    vector<int> n;
    int t;
    while(cin>>t)
        all.push_back(t);
    sort(all.begin(),all.end());
    t=all[0];
    int k=0;
    for(int i=0;i<all.size();i++){
        if(t==all[i])
            k++;
        else
        {
            s.push_back(t);
            n.push_back(k);
            t=all[i];
            k=1;
        }
    }
    s.push_back(t);
    n.push_back(k);
    int max=0;
    for(t=0;t<n.size();t++)
        if(max<n[t])
            max=n[t];
    for(t=0;t<n.size();t++)
        if(n[t]==max)
            cout<<"the most number is "<<s[t]<<endl;

    while(1);
    return 0;
}

#include "../../st.h"

int main()
{
    vector<string> names;
    vector<double> scores;
    string t;
    double n;
    int i;
    while(1)
    {
        cout<<"input name: ";
        cin>>t;

        if(t=="no"){
            cin>>t;
            break;
        }
        for(i=0;i<names.size();i++)
            if(names[i]==t){
                cout<<"this is error";
                exit(1);
            }
        names.push_back(t);
        cout<<"input scores:";
        cin>>n;
        scores.push_back(n);

    }
    for(i=0;i<names.size();i++)
        cout<<names[i]<<"-"<<scores[i]<<endl;
    cout<<endl;

    cout<<"input the name:";
    cin>>t;
    int f=0;
    for(i=0;i<names.size();i++)
        if(t==names[i]){
            f=1;
            break;
        }
    if(f==1)
        cout<<t<<"'s score is "<<scores[i]<<endl;
    else
        cout<<"not found."<<endl;

    cout<<"input the score:";
    cin>>n;
    f=0;
    for(i=0;i<scores.size();i++)
        if(n==scores[i]){
            f=1;
            cout<<names[i]<<endl;
        }
    if(f==0)
        cout<<"score not found."<<endl;

    while(1);
    return 0;
}    

//第六章习题4  一个vector取代两个vector
#include "../../st.h"

class Name_value{
public:
    string name;
    double val;

    Name_value(string s,double d);
};

Name_value::Name_value(string s,double d)
{
    name=s;
    val=d;
}

int main()
{
    vector<Name_value> nv;
    string s;
    double d;
    int i;
    while(1)
    {
        cout<<"input name: ";
        cin>>s;

        if(s=="no")
        {
            cin>>s;
            break;
        }
        for(i=0;i<nv.size();i++)
            if(nv[i].name==s)
            {
                cout<<"this is error";
                exit(1);
            }
        cout<<"input scores:";
        cin>>d;
        Name_value nv1(s,d);
        nv.push_back(nv1);
    }
    for(i=0;i<nv.size();i++)
        cout<<nv[i].name<<"-"<<nv[i].val<<endl;
    cout<<endl;

    cout<<"input the name:";
    cin>>s;
    int f=0;
    for(i=0;i<nv.size();i++)
        if(s==nv[i].name){
            f=1;
            break;
        }
    if(f==1)
        cout<<s<<"'s score is "<<nv[i].val<<endl;
    else
        cout<<"not found."<<endl;

    cout<<"input the score:";
    cin>>d;
    f=0;
    for(i=0;i<nv.size();i++)
        if(d==nv[i].val){
            f=1;
            cout<<nv[i].name<<endl;
        }
    if(f==0)
        cout<<"score not found."<<endl;

    while(1);

    return 0;
}

总的来说  这一章是很容易的  理解了就OK