Accelerated C++ 学习笔记及题解----第三章

本章主要内容

1.类型定义typedef

2.局部变量

3.格式化输出初涉

4.向量vector及基本方法

本章主要程序代码

1.计算平均成绩

#include <iomanip>#include <iostream>#include <string>using namespace std;int main(){// ask for and read the student's name    cout << "Please enter your first name: ";    string name;    cin >> name;    cout << "Hello, " << name << "!" << endl;// ask for and read the midterm and final grades    cout << "Please enter your midterm and final exam grades: ";    double midterm, final;    cin >> midterm >> final;// ask for the homework grades    cout << "Enter all your homework grades, "         "followed by end-of-file: ";// the number and sum of grades read so far    int count = 0;    double sum = 0;// a variable into which to read    double x;// invariant:// we have read `count' grades so far, and// `sum' is the sum of the first `count' grades    while (cin >> x)    {        ++count;        sum += x;    }// write the result    streamsize prec = cout.precision();    cout << "Your final grade is " << setprecision(3)         << 0.2 * midterm + 0.4 * final + 0.4 * sum / count         << setprecision(prec) << endl;    return 0;}

结果:

2.计算成绩中值

#include <algorithm>#include <iomanip>#include <iostream>#include <string>#include <vector>using namespace std;int main(){// ask for and read the student's name    cout << "Please enter your first name: ";    string name;    cin >> name;    cout << "Hello, " << name << "!" << endl;// ask for and read the midterm and final grades    cout << "Please enter your midterm and final exam grades: ";    double midterm, final;    cin >> midterm >> final;// ask for and read the homework grades    cout << "Enter all your homework grades, "         "followed by end-of-file: ";    vector<double> homework;    double x;// invariant: `homework' contains all the homework grades read so far    while (cin >> x)        homework.push_back(x);// check that the student entered some homework grades#ifdef _MSC_VER    typedef std::vector<double>::size_type vec_sz;#else    typedef vector<double>::size_type vec_sz;#endif    vec_sz size = homework.size();    if (size == 0)    {        cout << endl << "You must enter your grades. "             "Please try again." << endl;        return 1;    }// sort the grades    sort(homework.begin(), homework.end());// compute the median homework grade    vec_sz mid = size/2;    double median;    median = size % 2 == 0 ? (homework[mid] + homework[mid-1]) / 2             : homework[mid];// compute and write the final grade    streamsize prec = cout.precision();    cout << "Your final grade is " << setprecision(3)         << 0.2 * midterm + 0.4 * final + 0.4 * median         << setprecision(prec) << endl;    return 0;}

结果:

习题答案

3.2

#include <algorithm>#include <iostream>#include <vector>using namespace std;int main(){    vector<int> integers;    cout << "Integers: ";    int x;    while (cin >> x)        integers.push_back(x);    if (integers.size() == 0)    {        cout << endl << "No integers!" << endl;        return 1;    }    sort(integers.rbegin(), integers.rend());    typedef vector<int>::size_type vec_sz;    cout << "1st quartile" << endl;    for (vec_sz i = 0; i < integers.size() / 4; ++i)        cout << integers[i] << endl;    cout << "2nd quartile" << endl;    for (vec_sz i = integers.size() / 4; i < integers.size() / 2; ++i)        cout << integers[i] << endl;    cout << "3rd quartile" << endl;    for (vec_sz i = integers.size() / 2; i < integers.size() * 3 / 4; ++i)        cout << integers[i] << endl;    cout << "4th quartile" << endl;    for (vec_sz i = integers.size() * 3 / 4; i < integers.size(); ++i)        cout << integers[i] << endl;    return 0;}

结果:

3.3

#include <iostream>#include <string>#include <vector>using namespace std;int main(){    typedef vector<string>::size_type vec_sz;    vector<string> words;    vector<int> counts;    cout << "Words: ";    string s;    while (cin >> s)    {        bool found = false;        for (vec_sz i = 0; i < words.size(); ++i)        {            if (s == words[i])            {                ++counts[i];                found = true;            }        }        if (!found)        {            words.push_back(s);            counts.push_back(1);        }    }    for (vec_sz i = 0; i < words.size(); ++i)        cout << words[i] << " appeared " << counts[i] << " times" << endl;    return 0;}

结果:

3.4

#include <iostream>#include <string>using namespace std;int main(){    typedef string::size_type str_sz;    string longest;    str_sz longest_length = 0;    string shortest;    str_sz shortest_length = 0;    cout << "Words: ";    string s;    while (cin >> s)    {        if (longest_length == 0 || s.size() > longest_length)        {            longest = s;            longest_length = s.size();        }        if (shortest_length == 0 || s.size() < shortest_length)        {            shortest = s;            shortest_length = s.size();        }    }    cout << "Longest: " << longest << endl;    cout << "Shortest: " << shortest << endl;    return 0;}

3.5

#include <iomanip>#include <iostream>#include <string>#include <vector>using namespace std;#define NUM_HOMEWORK 2using std::vector;int main(){    vector<string> names;    vector<double> final_grades;    bool done = false;    while (!done)    {        // ask for and read the student's name        cout << "Please enter your first name: ";        string name;        cin >> name;        cout << "Hello, " << name << "!" << endl;        names.push_back(name);        // ask for and read the midterm and final grades        cout << "Please enter your midterm and final exam grades: ";        double midterm, final;        cin >> midterm >> final;        // ask for the homework grades        cout << "Enter both your homework grades, "             "followed by end-of-file: ";        // he number and sum of grades read so far        int count = 0;        double sum = 0;        // a variable into which to read        double x;        // invariant:        // we have read `count' grades so far, and        // `sum' is the sum of the first `count' grades        while (count < NUM_HOMEWORK)        {            ++count;            cin >> x;            sum += x;        }        double final_grade = 0.2 * midterm + 0.4 * final + 0.4 * sum / count;        final_grades.push_back(final_grade);        cout << "More? (Y/N) ";        string s;        cin >> s;        if (s != "Y")            done = true;    }    for (vector<string>::size_type i = 0; i < names.size(); ++i)    {        // write the result        streamsize prec = cout.precision();        cout << names[i] << "'s final grade is " << setprecision(3)             << final_grades[i]             << setprecision(prec) << endl;    }    return 0;}

3.6

#include <iomanip>#ifndef __GNUC__#include <ios>#endif#include <iostream>#include <string>using namespace std;int main(){// ask for and read the student's name    cout << "Please enter your first name: ";    string name;    cin >> name;    cout << "Hello, " << name << "!" << endl;// ask for and read the midterm and final grades    cout << "Please enter your midterm and final exam grades: ";    double midterm, final;    cin >> midterm >> final;// ask for the homework grades    cout << "Enter all your homework grades, "         "followed by end-of-file: ";// the number and sum of grades read so far    int count = 0;    double sum = 0;// a variable into which to read    double x;// invariant:// we have read `count' grades so far, and// `sum' is the sum of the first `count' grades    while (cin >> x)    {        ++count;        sum += x;    }    double homework_grade = (count > 0) ? sum / count : 0.0;// write the result    streamsize prec = cout.precision();    cout << "Your final grade is " << setprecision(3)         << 0.2 * midterm + 0.4 * final + 0.4 * homework_grade         << setprecision(prec) << endl;    return 0;}