4-0本章程序
//4.1 计算一位同学的分数
#include <iomanip>
#include <ios>
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <stdexcept>
using namespace std;
double median(vector<double> vec);
double grade(double midterm,double terminal,double homework);
double grade(double midterm, double terminal, const vector<double>&hw);
istream& read_hw(istream& in, vector<double>& hw);
int main()
{
cout << "please enter your first name: ";
string name;
cin >> name;
cout << "hello, " << name << "!" << endl;
cout << "please enter your midterm and terminal grades: ";
double midterm, terminal;
cin >> midterm >> terminal;
cout << "enter all your homework grades: "
<< "followed by end-of-file: ";
vector<double>homework;
read_hw(cin, homework);
try{
double final_grade = grade(midterm,terminal, homework);
streamsize prec = cout.precision();
cout << "your final grade is: " << setprecision(3)
<< final_grade << setprecision(prec) << endl;
}
catch (domain_error){
cout << endl << "you must enter your grades: "
"please enter again." << endl;
return 1;
}
return 0;
}
double median(vector<double> vec)
{
typedef vector<double>::size_type vec_sz;
vec_sz size = vec.size();
vec_sz mid = size / 2;
if (size == 0){
throw domain_error("median of an empty vector");
}
sort(vec.begin(), vec.end());
return size % 2 == 0 ? (vec[mid] + vec[mid - 1]) / 2 : vec[mid];
}
double grade(double midterm, double terminal, double homework)
{
return midterm*0.2 + terminal*0.4 + homework*0.4;
}
double grade(double midterm, double terminal, const vector<double>&hw)
{
if (hw.size() == 0)
throw domain_error("no homework! ");
return grade(midterm, terminal, median(hw));
}
istream& read_hw(istream& in, vector<double>& hw)
{
if (in){
hw.clear();
double x;
while (in >> x){
hw.push_back(x);
}
in.clear();
}
return in;
}
//4.2 计算多位同学的成绩
//median.h
#ifndef _MEDIAN_H_
#define _MEDIAN_H_
#include <vector>
double median(std::vector<double>);
#endif
//median.c
#include <algorithm>
#include <stdexcept>
#include "median.h"
using namespace std;
double median(vector<double> vec)
{
typedef vector<double>::size_type vec_sz;
vec_sz size = vec.size();
vec_sz mid = size / 2;
if (size == 0){
throw domain_error("median of an empty vector");
}
sort(vec.begin(), vec.end());
return size % 2 == 0 ? (vec[mid] + vec[mid - 1]) / 2 : vec[mid];
}
//student_info.h
#ifndef _STUDENT_INFO_H
#define _STUDENT_INFO_H
#include <string>
#include <vector>
#include <iostream>
struct student{
std::string name;
double midterm, terminal;
std::vector<double> homework;
};
bool campare(const student&, const student&);
std::istream& read(std::istream&, student&);
std::istream& read_hw(std::istream&,std::vector<double>&);
#endif
//student_info.c
#include "student_info.h"
using namespace std;
bool campare(const student& x, const student& y)
{
return x.name < y.name;
}
std::istream& read(std::istream& is, student& s)
{
is >> s.name >> s.midterm >> s.terminal;
read_hw(is, s.homework);
return is;
}
std::istream& read_hw(std::istream& is, std::vector<double>& hw)
{
if (is){
hw.clear();
double x;
while (is >> x){
hw.push_back(x);
}
is.clear();
}
return is;
}
//grade.h
#ifndef _GRADE_H
#define _GRADE_H
#include <vector>
#include "student_info.h"
double grade(double, double, double);
double grade(double, double, std::vector<double>&);
double grade(const student&);
#endif
//grade.c
#include <stdexcept>
#include "grade.h"
#include "median.h"
using namespace std;
double grade(double midterm, double terminal, double homework)
{
return midterm*0.2 + terminal*0.4 + homework*0.4;
}
double grade(double midterm, double terminal, const vector<double>&hw)
{
if (hw.size() == 0)
throw domain_error("no homework! ");
return grade(midterm, terminal, median(hw));
}
double grade(const student& s)
{
return grade(s.midterm, s.terminal,s.homework);
}
//main.c
#include <algorithm>
#include <iomanip>
#include <stdexcept>
#include "student_info.h"
#include "grade.h"
using namespace std;
int main()
{
vector<student> students;
student record;
string::size_type maxlen = 0;
while (read(cin, record)){
maxlen = max(maxlen, record.name.size());
students.push_back(record);
}
sort(students.begin(), students.end(), campare);
for (vector<student>::size_type i = 0; i != students.size(); ++i){
cout << students[i].name
<< string(maxlen + 1 - students[i].name.size(), ‘ ‘);
try{
double final_grade = grade(students[i]);
streamsize prec = cout.precision();
cout << setprecision(3) << final_grade
<< setprecision(prec);
}
catch (domain_error e){
cout << e.what();
}
cout << endl;
}
return 0;
}
关于read_hw函数的解释：
std::istream& read_hw(std::istream& is, std::vector<double>& hw)
{
if (is){
hw.clear();
double x;
while (is >> x){
hw.push_back(x);
}
is.clear();
}
return is;
}
首先两个参数都是传址调用，原因是输入流不能复制，只能用引用，而后面那个vector是我们要改变的值，所以要用引用；
if(is)的意思是判断流读取是否成功，如书中所受，当读入文件结束符，或者输入不兼容的值，或硬件问题会导致读取失败；
hw.clear()是清空vector<double>的值，使之为空向量；
is.clear()是重置流，作用是为了继续接收其他流格式，在read函数里的string name等等；
4-1max函数需要匹配，将
int maxlen改为string::size_type maxlen即可
4-2写一个程序，计算从1到100的所有整数的平方。程序输出两列：
第一列是1到100的整数值，第二列是整数值的平方。
使用setw函数来控制输出，使得这些值按列整齐排列。
#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
int count = 101;
for (int i = 1; i != count; i++){
cout <<left<< setw(3) << i << " "
<< i*i << endl;
}
return 0;
}
4-3如果我们上面的程序，计算从1到999的值的平方，但是没有改变setw的参数，
会发生什么呢？重写这个程序，使它更为灵活，在增加i的时候i的时候，不需要修改setw的参数。
（求出数字的位数）
#include <iostream>
#include <iomanip>
using namespace std;
int number(int );
int main()
{
int count = 115;
int num = number(count - 1);
cout << num << endl;
for (int i = 1; i != count; i++){
cout<<left<< setw(num) << i << " "
<< i*i << endl;
}
return 0;
}
int number(int x)
{
int num = 1;
while(x / 10 > 0){
num++;
x = x / 10;
}
return num;
}
4-4改变你的平方程序，使用double类型取代int类型，使用控制符来控制输出，使得这些值按列整齐输出
#include <iostream>
#include <iomanip>
using namespace std;
int digital(double);
int main()
{
double count = 99;
for (double i = 0; i < count; i += 0.5)
{
cout << left << setw(digital(count) + 2) << i
<<i*i<< endl;
}
return 0;
}
int digital(double x)
{
int count = 1;
int integer = x / 1;
while (integer != 0){
count++;
integer /= 10;
}
return count;
}
本来想用digital连同算出整数位加上小数位，思路是，把小数位分离出来，计算后乘以10移到整数位再减去整数位，
但是出现了问题，小数的加减乘除似乎不是那么精确和简单，所以最后采用保留两位小数的方法。
在网上看到其他求数位的方法：（用log10求数位）
#include <cmath>
#include <iomanip>
#include <iostream>
using namespace std;
int get_width(double n) {
return log10(n) + 1;
}
int main() {
double max = 1000.0;
for (double i = 1.0; i <= max; ++i) {
cout << setw(get_width(max))
<< i
<< setw(get_width(max * max) + 1)
<< i * i
<< endl;
}
return 0;
}
4-5写一个函数，从输入流中读取单词，并把单词保存在一个vector中，然后使用这个函数写一个程序，计算
输入中单词的数目，并计算 每个单词出现的次数（计算单词出现次数参考第三章练习）
#include <iostream>
#include <iomanip>
#include <vector>
#include <string>
using namespace std;
int count(istream& , vector<string>&);
int frequency(vector<string>&,vector<string>&);
int main()
{
cout << "please input the text: " << endl;
vector<string> text;
int number;
number = count(cin, text);
vector<string> temp;
cout << "this text has " << number << " words" << endl;
frequency(text, temp);
int count;
for (int i = 0; i != temp.size(); i++){
count = 0;
for (int j = 0; j != text.size(); j++){
if (temp[i] == text[j]){
count++;
}
}
cout << "the word: " << temp[i] << " "
<< count << " times" << endl;
}
return 0;
}
int count(istream& in, vector<string>& text)
{
int num = 0;
if (in){
text.clear();
string word;
while (in >> word){
text.push_back(word);
num++;
}
in.clear();
}
return num;
}
int frequency(vector<string>&text, vector<string>&temp)
{
int i, j;
for (i = 0; i != text.size(); i++){
for (j = 0;; j++){
if (j == temp.size()){
temp.push_back(text[i]);
break;
}
else{
if (temp[j] == text[i])
break;
}
}
}
return 1;
}
4-6重写student_info结构来直接计算成绩，并且在student_info结构中只保存最终成绩
//median.h and median.c needn‘t change
//student_info.h has change struct student:
struct student{
std::string name;
double final_grade;
};
//student_info.c has change the function of read
std::istream& read(std::istream& is, student& s)
{
double midterm, terminal;
is >> s.name >> midterm >> terminal;
vector<double>homework;
read_hw(is, homework);
if (is)
s.final_grade = grade(midterm, terminal, homework);
return is;
}
//grade.h has no change and grade.c change last function
double grade(student& s)
{
return s.final_grade;
}
//main.c
#include <algorithm>
#include <iomanip>
#include <stdexcept>
#include "student_info.h"
#include "grade.h"
using namespace std;
int main()
{
vector<student> students;
student record;
string::size_type maxlen = 0;
while (read(cin, record)){
maxlen = max(maxlen, record.name.size());
students.push_back(record);
}
sort(students.begin(), students.end(), campare);
for (vector<student>::size_type i = 0; i != students.size(); ++i){
cout << students[i].name
<< string(maxlen + 1 - students[i].name.size(), ‘ ‘);
try{
streamsize prec = cout.precision();
cout << setprecision(3) << students[i].final_grade
<< setprecision(prec);
}
catch (domain_error e){
cout << e.what();
}
cout << endl;
}
return 0;
}
4-7写一个程序计算保存在vector<double>对象中的数值的平均值
#include <iostream>
#include <vector>
using namespace std;
double average(vector<double> );
int main()
{
vector<double> vec;
double x;
while (cin >> x){
vec.push_back(x);
}
cout << "the average is :" <<
average(vec)<<endl;
}
double average(vector<double> vec)
{
if (vec.size() == 0)
throw domain_error("the vector is empty!");
double sum = 0;
for (vector<double>::size_type i = 0; i != vec.size(); i++){
sum += vec[i];
}
return sum / vec.size();
}
时间： 2024-10-13 16:37:29