无聊之重学c/c++

#include <iostream>

#include <iomanip>
#include<stdio.h>
#include<string>
#include <fstream>

using namespace std;

int main()
{
    double r, s, l;
    cin >> r;
    s = 3.14 * r * r;
    l = 2 * 3.14 * r;
    cout << "面积=" << s << endl;
    cout <<"\n" << endl;
    cout   << "周长=" << l << endl;
    system("pause");
    return 0;
    //std::cout << "Hello World!\n";
}

int main() 
{
    float r = 3.0, s, l;
    l = 2 * PI * r;
    s = PI * r * r;
    cout << "l=" << l << "\ns=" << s << endl;
    system("pause");
    return 0;
}
int main()
{
    double f, c;
    cout << "华氏温度=" << endl;
    cin >> f;
    c = 5 / 9.00 * (f - 32);
    cout << "换算的摄氏温度=" << c << endl;
    system("pause");
    return 0;

}

int main() {
    int i = 3, j;
    j = ++i;
    cout << "i+" << i << '\t' << "j=" << j << endl;
    i = 3;
    j = i++;
    cout << "i=" << i << "\t" << "j=" << j << endl;
    system("pause");
    return 0;

}


int main() {
    int  a = 38;
    float b;
    b = float(a);
    cout << b << endl;
    system("pause");
    return 0;
}

int main() {
    double a, b, c, p, s;
    cin >> a >> b >> c;
    p = (a + b + c) / 2;
    s = sqrt(p * (p - a) * (p - b) * (p - c));
    cout << "三角形面积为：" << s << endl;
    system("pause");
    return 0;
}

int main() {
    double a, b, c, p, s;
    cin >> a >> b >> c;
    if (a + b > c && a + c > b && b + c > a)
    {
        p = (a + b + c) / 2;
        s = sqrt(p * (p - a) * (p - b) * (p - c));
        cout << "三角形面积:" << s << endl;
    }
    else
        cout << "输入数值不能组成三角形" << endl;

}


int main() {
    double a, b, c, p, s;
    cin >> a >> b >> c;
    while (!(a + b > c && a + c > b && b + c > a))
    {
        cout << "输入有误,再次输入" << endl;
        cin >> a >> b >> c;
       
    }
    p = (a + b + c) / 2;
    s = sqrt(p * (p - a) * (p - b) * (p - c));
    cout << "三角形面积:" << s << endl;
}

int main() {
    char sex, group;
    int age;
    cout << "input sex（f or m ）and age:" << endl;
    cin >> sex >> age;
    if (sex == 'm')
        if (age < 40) group = 'A'; else group = 'B';
    else
        if (age < 40) group = 'C'; else group = 'D';
    cout << "group=" << group << endl;
}


int main() {
    int mark;
    char grade;
    cout << "input mark (0-100);" << endl;
    cin >> mark;
    switch (mark / 10) {
    case 10:
    case 9: grade = 'A'; break;
    case 8: grade = 'B'; break;
    case 7: grade = 'C'; break;
    case 6: grade = 'D'; break;
    default: grade = 'E';
    }
    cout << "mark=" << mark << ",grade=" << grade << endl;
    system("pause");
    return 0;
}

int main() {
    int i(1), sum(0);
    while (i < 100) {
        sum = sum + i;
        i = i + 2;
    }
    cout << "s=" << sum << endl;
    system("pause");
    return 0;
}

int main() {
    int i(1), sum(0);
    do {
        sum = sum + i;
        i =i + 2;

    } while (i < 100);

    cout << "sum=" << sum << endl;
    system("pause");
    return 0;
}


int main() {
    int i(1), sum(0);
    for (i; i < 100;i=i+2) {
        sum = sum + i;
    }
    cout << "sum=" << sum << endl;
    system("pause");
    return 0;
}


int main() {
    int i(1), sum(0);
    for ( ; ;) {
        if (i >= 100)
            break;
        sum = sum + i;
        i = i + 2;
       
    }
    cout << "sum=" << sum << endl;
    system("pause");
    return 0;
}

//辗转相除求最大公约数
int main() {
    int m,n,r;
    do
    {
        cout << "input m,n" << endl;
        cin >> m >> n;

    } while (m <= 0 || n <0);
    while((r=m%n)!=0){
        m = n; n = r;

    }
    cout << "最大公约数为" << n << endl;
    system("pause");
    return 0;
}



//判断是否为素数
int main() {
    int k, m;
    cin >> m;
    for (k = 2; k < m; k++)
        if (m % k == 0)
            break;
    if (k==m)
        cout << m << "是素数" << endl;
    else
        cout << m << "不是素数" << endl;
    system("pause");
    return 0;
}

//打印九九乘法表
int main() {
    cout << "\t九九乘法表" << endl;
    for (int i = 1; i <= 9; i++) {
        for (int j = 1; j <= i; j++)
            cout << i << "x" << j << "=" << i * j << "\t";
        cout << endl;
    }

    system("pause");
    return 0;
}


//判断是否为素数
int main() {
    int k, m,number(0);
   for(k=2;k<=100;k++)
   {
        for (m = 2; m < k; m++)
        if (k % m == 0)
            break;
    if (k == m) 
    {
        cout << m << "是素数" << "\t";
        number++;
        if (number%5==0)
            cout << endl;
    }
    
    }
    system("pause");
    return 0;
}


//数组
int main() {
    int i, k = 0;
    float s[3], ave, sum=0;
    for (i=0; i < 3; i++) {
        cin >> s[i];
        sum = sum + s[i];
    }
    ave = sum / 3;
    for (i = 0; i < 3; i++)
        if (s[i] > ave)
            k++;
    cout << "总成绩=" << sum <<"平均成绩="<<ave<< endl;
    system("pause");
    return 0;
}


//进制转换
int main() {
    int i = 0, r, n, a[10];
    char b[16] = { '0','1','3','4','5','6','7','8','9','A','B','C','D','E','F' };
    cin >> n >> r;
    do {
        a[i] = n % r;
        n = n / r;
        i++;
    } while (n != 0);
    for (--i; i >= 0; --i) {
        n = a[i];
        cout << b[n];
    }
    system("pause");
    return 0;
}

//数组求最大数
int main() {
    int a[10], i, max;
    for (i = 0; i < 10; i++) {
        a[i] = rand() % 101;
        cout << a[i] << endl;
    }
    max = a[0];
    for (i = 1; i < 10; i++)
        if (max<a[i])
            max=a[i];
    cout << "max=" << max << endl;
    system("pause");
    return 0;
}

//选择排序
int main() {
    int arr[10],k,t,imax;
    for (int i = 0; i < 10; i++) {
        arr[i] = rand() % 101;
    }
    for (int j = 0; j < 10; j++)
    {
         imax = j;
        for (int k = j + 1; k < 10; k++)
            if (arr[k] > arr[imax])
                imax = k;
             t = arr[imax];
            arr[imax] = arr[j];
            arr[j] = t;
    }
    
    for (int h = 0; h < 10; h++)
    {
        cout << arr[h] << "\t";
    }
   
    cout << endl;

    system("pause");
    return 0;
}
//冒泡排序
int main() {
    int arr[10],t;
    for (int i = 0; i < 10; i++) {
        arr[i] = rand() % 101;
    }

    for (int k=0; k < 9; k++) {

        for (int j = 0; j < (9 - k); j++)
            if (arr[j] >= arr[j + 1])
            {
                t = arr[j];
                arr[j] = arr[j + 1];
                arr[j + 1] = t;
            }
    }
   
    for (int h = 0; h < 10; h++)
    {
        cout << arr[h] << "\t";
    }
    cout << endl;

    system("pause");
    return 0;
}



//数组插入
int main() {
    //排序
    int arr[10], t;
    int x, f, post;

    for (int i = 0; i < 10; i++) {
        arr[i] = rand() % 101;
    }

    for (int k = 0; k < 9; k++) {

        for (int j = 0; j < (9 - k); j++)
            if (arr[j] >= arr[j + 1]){
                t = arr[j];
                arr[j] = arr[j + 1];
                arr[j + 1] = t;
            }
    }
    
    
    
    //插入
   
    cout << "输入要插入的数据=";
    cin >> x;
    
    for (f = 0; f < 10; f++) 
        if (x < arr[f])
            break;
        post = f;
        for (f = 9; f >= post; f--)
            arr[f + 1] = arr[f];
        arr[post] = x;
   

    
    for (int h = 0; h < 11; h++)
    {
        cout << arr[h] << "\t";
    }
    cout << endl;

    system("pause");
    return 0;

}

//数组二分法查找
int main() {
    int arr[10],low(0), high(9),mid,x;
    
    //数组加1-100随机数
    for (int i = 0; i < 10; i++) {
        arr[i] = rand() % 101;
    }
    //数组排序
    for (int k = 0; k < 9; k++) {
        for (int j = 0; j < (9 - k); j++)
            if (arr[j] >= arr[j + 1])
            {
                int t = arr[j];
                arr[j] = arr[j + 1];
                arr[j + 1] = t;
            }
    }

    //打印要排序的数组
    for (int h = 0; h < 10; h++)
    {
        cout << arr[h] << "\t";
    }
    cout << endl;

    //输入要查找的数字
    cout << "输入要查找的数据=";
    cin >> x;

    while (low<=high) {
       mid = (low + high) / 2;
        if (x == arr[mid])
            break;
        else if (x > arr[mid])
            low = mid + 1;
        else
            high = mid - 1;
    }
    
    if (low > high)
        cout << "没找到" << endl;
    else
        cout << "找到的数字下标为=" << mid << endl;

    system("pause");
    return 0;
}

//二维数组，打印杨辉三角形
int main() {
    int arr[10][10];
    for (int i = 0; i < 10; i++)
        arr[i][0] = arr[i][i] = 1;
    
    
    for (int i=2;i<10;i++)
        for (int j=1;j<i;j++)
            arr[i][j] = arr[i - 1][j - 1] + arr[i - 1][j];


    for (int i = 0; i < 10; i++) {
    
        for (int j = 0; j < i; j++)
            cout << arr[i][j] << ' ';
        cout << endl;
    }

    system("pause");
    return 0;
}

//FLOYD最短路径算法
int main() {
    int e[4][4],N(4),M(8), MAX(9999),i, j, k, st, en, d;
    for (i = 0; i < N; i++)
        for (j=0; j < N; j++)
            if (i==j)
                e[i][j] = 0;
            else
                e[i][j]=MAX;
    for (i = 1; i <= M; i++)
    {
        cin >> st >> en >> d;
                 e[st][en]=d;
    }
    for (k = 0; k < N; k++)
        for (i = 0; i < N; i++)
            for (j = 0; j < N; j++)
                if (e[i][j] > e[i][k] + e[k][j])
                    e[i][j] = e[i][k] + e[k][j];
    for (i = 0; i < N; i++)
    {
        for (j = 0; j < N; j++)
            cout << (char)('A' + i) << "->" << (char)('A' + j) << ";" << e[i][j] << "\t";
        cout << endl;


    }

    system("pause");
        return 0;
}


//字符串
int main() {
    char s[100];
    
    cin >> s;
    cout << s << endl;


    system("pause");
    return 0;


}


int main() {
    char s[100];
    gets_s(s);
    puts(s);
    system("pause");
    return 0;
}

//字符大小写转换
int main() {
    char s[10];
    int i;
    gets_s(s);
    for (i = 0; s[i] != '\0'; i++)
        if (s[i] >= 'a' && s[i] <= 'z')
            s[i] = s[i] - 'a' + 'A';
    puts(s);
    system("pause");
    return 0;
}

int main() {
    int a[10],i, *p = a;
    for (i = 0; i < 5; i++)
        cin >> *p++;
    for (i = 0; i < 5; i++)
        cout << p[i] <<' ';
    system("pause");
    return 0;
}

//地址
int main() {
    int a[3] = { 10,20,30 }, * p;
    p = a;
    cout << *p++ << endl;
    cout << *p << endl;
    system("pause");
    return 0;
}

//值增加
int main() {
    int a[3] = { 10,20,30 }, * p;
    p = a;
    cout << ( * p)++ << endl;
    cout << *p << endl;
    system("pause");
    return 0;
}

int main() {
    char *p, *q;
    p = new char[100];
    gets(p);
    q = p;
    cout << "输入每个字符；";
    while (*p!='\0')
        cout << *P++ << ' ';
    cout << "\n字符串长度；"<<p-q <<endl;
    system("pause");
    return 0;
}

//函数
float area(float x, float y, float z)
{
    float c, s;
    c = (x + y + z) / 2;
    s = sqrt(c * (c - x) * (c - y) * (c - z));
    return s;
}

int main() {
    float a, b, c, d, e, f, g, s;
    cin >> a >> b >> c >> d >> e >> f >> g >> s;
    s = area(a, b, c) + area(c, d, e) + area(e, f, g);
    cout << s << endl;
    system("pause"); return 0;

}
//打印星星
void pic() {
    for (int i=0;i<5;i++)
    {
        cout << setw(10 - i);
        for (int j = 0; j < 2 * i + 1; j++)cout << "*";
        cout << endl;
    }
    return;
}

int main() {
    pic(); pic();
    system("pause"); return 0;

}

//降序数判断

bool drop(int n,int &sum) {
    int x = n;
    bool flag = 1;
    while (n >= 10 && flag)
        if (n / 10 % 10 < n % 10)
            flag = 0; else n /= 10;
    while (x)
    {
        sum += x % 10; x /= 10;
    }
    return flag;
}

int main() {
    int m, sum1 = 0;
    cin >> m;
    if (drop(m, sum1))
        cout << m << "___yes" << endl;
    else
        cout << m << "___no" << endl;
    cout << "各位数之和；" << sum1 << endl;

}

//数组作为函数参数
void sort(int a[],int n) {
    int i, j, k, w;
    for (i = 0; i < n - 1; i++)
    {
        k = i;
        for (j = i + 1; j < n; j++) if (a[k] < a[j])k = j;
        if (i != k) { w = a[i]; a[i] = a[k]; a[k] = w; }
    }
}

//递归二分查找
int Binary_Search(int low, int high, int key) {
    if (low > high) return -1;
    int mid = (low + high)/2;
    if (key==a[mid])
        return mid;
    else if (key < a[mid])
        return Binary_Search(low, mid -1,key);
    else
        return Binary_Search(mid + 1, high,key);
}


//结构数据类型
#define N 2
struct Student {
    char name[10];
    char no[7];
    double Chinese, English, Math, avg;
};

int main() {
    int i, j;
    Student s[N], t;
    for (i = 0; i < N; i++)
    {
        cin >> s[i].name >> s[i].no >> s[i].Chinese >> s[i].English >> s[i].Math;
        s[i].avg = (s[i].Chinese + s[i].English + s[i].Math) / 3;
    };

    for(i=0;i<N-1;i++)
        for(j=0;j<N-1-i;i++)
            if (s[j].avg > s[j + 1].avg)
            {
                t = s[j];
                s[j] = s[j + 1];
                s[j + 1] = t;
            }
    for (i = 0; i < N; i++) {
        cout << s[i].name << "  " << s[i].no << "   "<<s[i].Chinese << "    ";
        cout << s[i].English << "   " << s[i].Math << " " << s[i].avg << endl;
    }
    system("pause");
    return 0;

}

//链表
struct node* create(int n) {
    struct node *head = NULL;
    struct node *tail, *newnode;
    for (int i = 0; i < n; i++)
    {
        newnode = new node;
        cin >> newnode->data;
        if (head == NULL)
            head = newnode;
        else
            tail->next = newnode;
        tail = newnode;


    }
    tail->next = NULL;
    return(head);
}
//指针后移
void print(struct node, *head)
{
    struct node *p = head;
    while (p != NULL) 
    {
        cout << p->data << "\t";
        p = p->next;
    }
}
//链表查找
void search(tructnode *head, int i){
    int j = 1;
    struct node* p = head;
    if (i < 1)
        cout << "illegal index\n";
    else
    {
        while (j!=i&&p!=NULL)
        {
            j++;
            p = p->next;
        }
        if (j == i && p != NULL)
            cout << p->data;
        else
            cout << "illegal index \n";
    }

}

//文件操作
int main() {
    FILE *fp1, *fp2;
    char ch;
    fp1 = fopen("c:\\text.txt", "r");
    if (fp1 == NULL)
    {
        cout << "can't open filel.txt"; exit(1);

    }
    if ((fp2 = fopen("c:\\texr2.txt", "w")) == NULL)
    {
        cout << "can't open file2"; fclose(fp1); exit(1);
    }
    while (!feof(fp1))
    {
        ch = fgetc(fp1);
        putchar(ch);
        if (ch >= '0' && ch <= '9')fputc(ch, fp2);

    }
    fclose(fp1); fclose(fp2);
    system("pause");
    return 0;
}

#define N 3
#include <iostream>
using namespace std;
struct student {
    char name[20];
    char num[8];
    double score;
};
int main() {
    struct student s[N], t[N];
    int i;
    FILE* fp;
    if ((fp = fopen("student.dat", "wb")) == NULL)
    {
        cout << "can't open student.dat";
        exit(1);
    }
    for (i = 0; i < N; i++)
    {
        cin >> s[i].name >> s[i].num >> s[i].score;
        fwrite(&s[i], sizeof(student), 1, fp);

    }
    fclose(fp);
    if ((fp = fopen("student.dat", "rb")) == NULL)
    {
        cout << "can't open student.dat";
        exit(1);
    }
    fread(t, sizeof(t), 1, fp);
    for (i = 0; i < N; i++)
        cout << t[i].name << " " << t[i].num << " " << t[i].score << endl;
    fclose(fp);
    system("pause");
    return 0;

}

//类和对象
class Circle {
private:
    double x, y, r;
public:
    void set(double x1, double y1, double r1)
    {
        x = x1; y = y1; r = r1;
    }
    void print() {
        cout << "圆心;(" << x << "," << y << ")" << "半径：" << r << endl;
    }
    double gettarea() {
        return 3.14 * r * r;
    }
    double getgirth()
    {
        return 2 * 3.14 * r;
    }
};

int main() {
    Circle c;
    c.set(0, 0, 2);
    c.print();
    cout << c.gettarea() << endl;
    cout << c.getgirth() << endl;
    return 0;

}
//常成员对象
class Time {
private:
    int hour, minute, second;
public:
    Time()
    {}
    Time(int h, int m, int s)
    {
        hour = h; minute = m; second = s;
    }
    void settime(int h, int m, int s)
    {
        hour = h; minute = m; second = s;
    }
    void print() const
    {
        cout << hour << ":" << minute << ":" << second << endl;
    }
};

int main() {
    int h, m, s;
    Time t1;
    const Time t2(10, 23, 34);
    cin >> h >> m >> s;
    t1.settime(h, m, s);
    t1.print();
    t2.print();
    system("pause");
    return 0;

}