---
title: 第五次作业（答案）
date: 2020-11-11 22:11:05
tags:
---


# P138-17

答案：A对Z，B对X，C对Y

```C
#include <stdio.h>

int main()
{
    int result[3] = { 0, 0, 0 }; // 分别表示ABC三人的对手

    // 分别给ABC指派对手
    for (int i = 0; i < 3; ++i) { // A
        result[0] = 'X' + i;
        for (int j = 0; j < 3; ++j) { // B
            result[1] = 'X' + j;
            for (int k = 0; k < 3; ++k) { // C
                result[2] = 'X' + k;
                // 检查合法性

                // 两人的对手不能一样
                if (result[0] == result[1]) {
                    continue;
                }
                if (result[0] == result[2]) {
                    continue;
                }
                if (result[1] == result[2]) {
                    continue;
                }

                // A不和X比
                if (result[0] == 'X') {
                    continue;
                }

                // C 不和X，Z比
                if (result[2] == 'X') {
                    continue;
                }
                if (result[2] == 'Z') {
                    continue;
                }

                // 剩下的就是正确答案
                printf("A的对手是%c\n", result[0]);
                printf("B的对手是%c\n", result[1]);
                printf("C的对手是%c\n", result[2]);
            }
        }
    }
    return 0;
}
```

# 二分查找

```C
#include <stdio.h>

int main()
{
    int a[100];

    printf("二分查找");
    int n;
    printf("请输入n：\nn = ");
    scanf("%d", &n);
    printf("请输入n个有序数（从小到大）：\n");
    for (int i = 0; i < n; ++i) {
        scanf("%d", a + i);
    }
    printf("请输入你要找的数：");
    int m;
    scanf("%d", &m);

    int l = 0;
    int r = n - 1;
    while (1) {
        if (l == r) {
            if (m == a[l]) {
                printf("a[%d] = %d\n", l, m);
            } else if (m < a[l]) {
                for (int i = n - 1; i >= l; --i) {
                    a[i + 1] = a[i];
                }
                a[l] = m;
                printf("%d被插入到了a[%d]的位置\n", m, l);
                for (int i = 0; i < n + 1; ++i) {
                    printf("a[%d] = %d\n", i, a[i]);
                }
            } else {
                for (int i = n - 1; i >= l + 1; --i) {
                    a[i + 1] = a[i];
                }
                a[l + 1] = m;
                printf("%d被插入到了a[%d]的位置\n", m, l + 1);
                for (int i = 0; i < n + 1; ++i) {
                    printf("a[%d] = %d\n", i, a[i]);
                }
            }
            break;
        } else if (r == l + 1) {
            if (m == a[l]) {
                printf("a[%d] = %d\n", l, m);
                break;
            } else if (m < a[l]) {
                for (int i = n - 1; i >= l; --i) {
                    a[i + 1] = a[i];
                }
                a[l] = m;
                printf("%d被插入到了a[%d]的位置\n", m, l);
                for (int i = 0; i < n + 1; ++i) {
                    printf("a[%d] = %d\n", i, a[i]);
                }
                break;
            } else {
                l++;
            }
        } else {
            int c = (l + r) / 2;
            if (m == a[c]) {
                printf("a[%d] = %d\n", c, m);
                break;
            } else if (m < a[c]) {
                r = c - 1;
            } else {
                l = c + 1;
            }
        }
    }

    return 0;
}
```

# P165-3

```C
#include <stdio.h>

int main()
{
    int a[3][3];
    printf("请输入一个3x3的矩阵：\n");
    for (int i = 0; i < 3; ++i) {
        for (int j = 0; j < 3; ++j) {
            scanf("%d", &a[i][j]);
        }
    }
    int sum = a[0][0] + a[0][2] + a[1][1] + a[2][0] + a[2][2];

    printf("对角线元素之和为%d\n", sum);

    return 0;
}
```

# P165-6

```C
#include <stdio.h>

int main()
{
    int a[10][10];
    for (int i = 0; i < 10; ++i) {
        a[i][0] = 1;
        a[i][i] = 1;
    }
    
    for (int i = 1; i < 10; ++i) {
        for (int j = 1; j < i; ++j) {
            a[i][j] = a[i - 1][j - 1] + a[i - 1][j];
        }
    }

    for (int i = 0; i < 10; ++i) {
        for (int j = 0; j <= i; ++j) {
            printf("%-5d", a[i][j]);
        }
        printf("\n");
    }
    
    return 0;
}
```

# P165-10

```C
#include <stdio.h>

int main()
{
    int upper = 0, lower = 0, num = 0, space = 0, others = 0;
    for (int i = 0; i < 80; ++i) {
        int c = getchar();

        if (c == ' ') {
            space++;
            continue;
        }
        if (c >= 'a' && c <= 'z') {
            lower++;
            continue;
        }
        if (c >= 'A' && c <= 'Z') {
            upper++;
            continue;
        }
        if (c >= '0' && c <= '9') {
            num++;
            continue;
        }
        others++;
    }
    printf("大写字母有%d\n", upper);
    printf("小写字母有%d\n", lower);
    printf("数字有%d\n", num);
    printf("空格%d\n", space);
    printf("其它字符有%d\n", others);
    return 0;
}
```