实验1
任务1
源代码task1.cpp
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#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
template<typename T>
void output(const T &c);
void test1();
void test2();
void test3();
int main() {
std::cout << "测试1: \n";
test1();
std::cout << "\n测试2: \n";
test2();
std::cout << "\n测试3: \n";
test3();
}
template <typename T>
void output(const T &c) {
for(auto &i : c)
std::cout << i << ' ';
std::cout << '\n';
}
void test1() {
using namespace std;
string s0{"0123456789"};
cout << "s0 = " << s0 << endl;
string s1(s0);
reverse(s1.begin(), s1.end());
cout << "s1 = " << s1 << endl;
string s2(s0.size(), ' ');
reverse_copy(s0.begin(), s0.end(), s2.begin());
cout << "s2 = " << s2 << endl;
}
void test2() {
using namespace std;
vector<int> v0{2, 0, 4, 9};
cout << "v0: "; output(v0);
vector<int> v1{v0};
reverse(v1.begin(), v1.end());
cout << "v1: "; output(v1);
vector<int> v2{v0};
reverse_copy(v0.begin(), v0.end(), v2.begin());
cout << "v2: "; output(v2);
}
void test3() {
using namespace std;
vector<int> v0{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
cout << "v0: "; output(v0);
vector<int> v1{v0};
rotate(v1.begin(), v1.begin()+1, v1.end());
cout << "v1: "; output(v1);
vector<int> v2{v0};
rotate(v2.begin(), v2.begin()+2, v2.end());
cout << "v2: "; output(v2);
vector<int> v3{v0};
rotate(v3.begin(), v3.end()-1, v3.end());
cout << "v3: "; output(v3);
vector<int> v4{v0};
rotate(v4.begin(), v4.end()-2, v4.end());
cout << "v4: "; output(v4);
}
问题回答
问题1：
reverse是反转字符串本身，例如reverse了s1后s1本身就被改变了，而reverse_copy是将字符串反转后的结果拷贝到另一格字符串中，原字符串本身依旧保持不变。
问题2：
相当于把整个元素区间分成两部分，将两部分整体前后调换，其中内部顺序不变。其三个参数依次为区间起始迭代器（包含该元素）、分隔迭代器（旋转后将成为第一个元素）、区间末尾迭代器（不包含该位置元素）
任务2
源代码task2.cpp
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#include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
#include <iomanip>
#include <cstdlib>
#include <ctime>
template<typename T>
void output(const T &c);
int generate_random_number();
void test1();
void test2();
int main() {
std::srand(std::time(0));
std::cout << "测试1: \n";
test1();
std::cout << "\n测试2: \n";
test2();
}
template <typename T>
void output(const T &c) {
for(auto &i: c)
std::cout << i << ' ';
std::cout << '\n';
}
int generate_random_number() {
return std::rand() % 101;
}
void test1() {
using namespace std;
vector<int> v0(10);
generate(v0.begin(), v0.end(), generate_random_number);
cout << "v0: "; output(v0);
vector<int> v1{v0};
sort(v1.begin(), v1.end());
cout << "v1: "; output(v1);
vector<int> v2{v0};
sort(v2.begin()+1, v2.end()-1);
cout << "v2: "; output(v2);
}
void test2() {
using namespace std;
vector<int> v0(10);
generate(v0.begin(), v0.end(), generate_random_number);
cout << "v0: "; output(v0);
auto min_iter = min_element(v0.begin(), v0.end());
auto max_iter = max_element(v0.begin(), v0.end());
cout << "最小值: " << *min_iter << endl;
cout << "最大值: " << *max_iter << endl;
auto ans = minmax_element(v0.begin(), v0.end());
cout << "最小值: " << *(ans.first) << endl;
cout << "最大值: " << *(ans.second) << endl;
double avg1 = accumulate(v0.begin(), v0.end(), 0.0) / v0.size();
cout << "均值: " << fixed << setprecision(2) << avg1 << endl;
sort(v0.begin(), v0.end());
double avg2 = accumulate(v0.begin()+1, v0.end()-1, 0.0) / (v0.size()-2);
cout << "去掉最大值、最小值之后，均值: " << avg2 << endl;
}
运行测试截图
问题回答
问题1
generate算法用于给迭代器区间的元素赋值，即填充整个区间。
问题2
遍历次数减少，效率更高，时间复杂度降低。
问题3
lambda为匿名函数，不需要单独定义，用完即可销毁。适用于临时、只适用一次的情况。
任务3
源代码task3.cpp
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#include <iostream>
#include <string>
#include <algorithm>
#include <cctype>
unsigned char func(unsigned char c);
void test1();
void test2();
int main() {
std::cout << "测试1: 字符串大小写转换\n";
test1();
std::cout << "\n测试2: 字符变换\n";
test2();
}
unsigned char func(unsigned char c) {
if(c == 'z')
return 'a';
if(c == 'Z')
return 'A';
if(std::isalpha(c))
return static_cast<unsigned char>(c+1);
return c;
}
void test1() {
std::string s1{"Hello World 2049!"};
std::cout << "s1 = " << s1 << '\n';
std::string s2;
for(auto c: s1)
s2 += std::tolower(c);
std::cout << "s2 = " << s2 << '\n';
std::string s3;
for(auto c: s1)
s3 += std::toupper(c);
std::cout << "s3 = " << s3 << '\n';
}
void test2() {
std::string s1{"I love cosmos!"};
std::cout << "s1 = " << s1 << '\n';
std::string s2(s1.size(), ' ');
std::transform(s1.begin(), s1.end(),
s2.begin(),
func);
std::cout << "s2 = " << s2 << '\n';
}
问题回答
问题1
实现字母向后循环移动1位，并区分了大小写两种情况。
问题2
tolower(c)是将大写字母转化成对应小写字母，如果本身就是小写字母则保持不变。toupper(c)是将小写字母转化为对应大写字母，如果本身就是大写字母则保持不变。
问题3
第一个参数是表示区间起始迭代器，第二个参数是区间末尾迭代器，第三个参数是目标容器的起始迭代器，最后一个参数是调用的函数对象，即对每一个元素执行这个函数。修改前源字符串保持不变，计算结果放入另一格字符串中，修改后计算结果直接覆盖源字符串，原始内容会丢失。
任务4
源代码task4.cpp
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#include <iostream>
#include <string>
#include <algorithm>
#include <cctype>
bool is_palindrome(const std::string &s);
bool is_palindrome_ignore_case(const std::string &s);
int main() {
using namespace std;
string s;
// 多组输入，直到按下Ctrl+Z结束测试
while(cin >> s) {
cout << boolalpha
<< "区分大小写: " << is_palindrome(s) << "\n"
<< "不区分大小写: " << is_palindrome_ignore_case(s) << "\n\n";
}
}
// 函数is_palindrome定义
bool is_palindrome(const std::string &s)
{
std::string rev=s;
reverse(rev.begin(), rev.end());
return rev == s;
}
// 函数is_palindrome_ignore_case定义
bool is_palindrome_ignore_case(const std::string &s)
{
std::string temp = s;
for(auto &ch : temp){
ch = tolower(static_cast<unsigned char>(ch));
}
std::string rev_temp = temp;
reverse(rev_temp.begin(), rev_temp.end());
return rev_temp == temp;
}
问题回答
问题1
可以把cin >> s 替换为 getline(cin,s)，getline(cin,s)会读取正行输入，可以接收空格。
任务5
源代码task5.cpp
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#include <iostream>
#include <string>
#include <algorithm>
std::string dec2n(int x, int n = 2);
int main() {
int x;
while(std::cin >> x) {
std::cout << "十进制: " << x << '\n'
<< "二进制: " << dec2n(x) << '\n'
<< "八进制: " << dec2n(x, 8) << '\n'
<< "十二进制: " << dec2n(x, 12) << '\n'
<< "十六进制: " << dec2n(x, 16) << '\n'
<< "三十二进制: " << dec2n(x, 32) << "\n\n";
}
}
// 函数dec2n定义
std::string dec2n(int x, int n){
if(x == 0){
return "0";
}
std::string res;
const char table[]="0123456789ABCDEFGHIJKLMNOPQRSTUV";
while(x > 0){
int rem = x % n;
res += table[rem];
x = x / n;
}
reverse(res.begin(), res.end());
return res;
}
任务6
源代码task6.cpp
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#include <iostream>
using namespace std;
int main(){
//表头
cout << " ";
for(int i=0; i<26; i++){
char ch = 'a'+i;
cout << ch << " ";
}
cout << endl;
for(int k=1; k<26; k++){
if(k<10)
cout << " " << k << " ";
else
cout << k << " ";
for(int i=0;i<26; i++){
char c='A'+(i+k)%26;
cout << c << " ";
}
cout << endl;
}
return 0;
}
任务7
源代码task7.cpp
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#include <iostream>
#include <cstdlib>
#include <ctime>
#include <iomanip>
#include <algorithm>
using namespace std;
int main()
{
srand(std::time(0)); // 添加随机种子
int right = 0;
for(int i=0; i<10; i++)
{
int op = rand() % 4;
int a = rand() % 10 + 1;
int b = rand() % 10 + 1;
int std_ans;
char opc;
if(op == 0)
{
opc = '+';
std_ans = a+b;
}
else if(op == 1)
{
opc = '-';
if(a<b)
swap(a,b);
std_ans = a-b;
}
else if(op == 2)
{
opc = '*';
std_ans = a*b;
}
else{
opc = '/';
while(a%b != 0){
a = rand()%10 + 1;
b = rand()%10 + 1;
}
std_ans = a/b;
}
int user_ans;
cout << a << " " << opc << " " << b << "=";
cin >> user_ans;
if(user_ans == std_ans){
right++;
}
}
double rate = right / 10.0;
cout << "正确率：" << fixed << setprecision(2) << rate *100 << "%" << endl;
return 0;
}
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