第六次作业和答案
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source/_posts/answer6.md
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---
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title: 第六次作业（答案）
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date: 2020-11-20 17:40:16
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tags:
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---
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# 冒泡排序
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```C
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#include <stdio.h>
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#include <stdlib.h>
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#include <time.h>
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#define LEN 10
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void swap(int a[], int i, int j)
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{
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int tmp = a[i];
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a[i] = a[j];
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a[j] = tmp;
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}
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void bubble_sort(int a[], int n)
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{
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int done = 0;
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for (int i = 0; i < n - 1; ++i) {
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if (done)
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return;
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done = 1;
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for (int j = 0; j < n - 1 - i; ++j) {
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if (a[j] > a[j + 1]) {
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swap(a, j, j + 1);
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done = 0;
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}
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}
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}
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}
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void rand_array(int a[], int n)
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{
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for (int i = 0; i < n; ++i) {
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int tmp = rand() % 20 + 1;
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a[i] = tmp;
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}
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}
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void print_array(int a[], int n)
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{
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for (int i = 0; i < n; ++i) {
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printf("%d ", a[i]);
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}
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printf("\n");
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}
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int main()
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{
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srand(time(0));
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int a[LEN];
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printf("使用随机数填充数组：\n");
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rand_array(a, LEN);
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print_array(a, LEN);
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bubble_sort(a, LEN);
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printf("排序过后的数组：\n");
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print_array(a, LEN);
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return 0;
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}
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```
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# 矩阵乘法
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```C
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#include <stdio.h>
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void input_matrix(double mat[][100], int *row, int *column)
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{
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printf("行：");
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scanf("%d", row);
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printf("列：");
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scanf("%d", column);
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printf("数据：\n");
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for (int i = 0; i < *row; ++i) {
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for (int j = 0; j < *column; ++j) {
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scanf("%lf", &mat[i][j]);
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}
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}
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}
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void print_matrix(double mat[][100], int row, int column)
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{
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for (int i = 0; i < row; ++i) {
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for (int j = 0; j < column; ++j) {
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printf("%f ", mat[i][j]);
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}
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printf("\n");
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}
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}
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void matrix_mul(double mat_a[][100], double mat_b[][100], double mat_c[][100],
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int a_row, int a_column, int b_column)
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{
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for (int i = 0; i < a_row; ++i) {
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for (int j = 0; j < b_column; ++j) {
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mat_c[i][j] = 0;
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for (int k = 0; k < a_column; ++k) {
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mat_c[i][j] += mat_a[i][k] * mat_b[k][j];
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}
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}
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}
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}
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int main()
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{
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double mat_a[100][100];
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double mat_b[100][100];
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double mat_c[100][100];
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int a_row;
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int a_column;
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int b_row;
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int b_column;
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printf("请输入矩阵A：\n");
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input_matrix(mat_a, &a_row, &a_column);
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printf("请输入矩阵B：\n");
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input_matrix(mat_b, &b_row, &b_column);
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if (a_column != b_row) {
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printf("A和B无法相乘！\n");
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return 0;
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}
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matrix_mul(mat_a, mat_b, mat_c, a_row, a_column, b_column);
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print_matrix(mat_c, a_row, b_column);
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return 0;
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}
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```
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# P166 T13
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```C
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#include <stdio.h>
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#include <string.h>
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void mystrcat(char a[], char b[])
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{
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int i = strlen(a) - 1;
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for (int j = 0; b[j] != '\n'; ++i, ++j) {
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a[i] = b[j];
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}
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a[i] = '\0';
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}
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int main()
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{
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printf("请输入第一个字符串，回车结束：\n");
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char a[200];
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fgets(a, 200, stdin);
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printf("请输入第二个字符串，回车结束：\n");
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char b[100];
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fgets(b, 100, stdin);
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mystrcat(a, b);
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printf("连接之后的字符串是\n%s\n", a);
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return 0;
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}
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```
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# P216 T13
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```C
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#include <stdio.h>
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double P(int n, double x)
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{
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if (n == 0) {
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return 1;
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} else if (n == 1) {
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return x;
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} else {
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return ((2 * n - 1) * x - P(n - 1, x) - (n - 1) * P(n - 2, x)) / n;
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}
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}
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int main()
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{
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printf("请输入x: ");
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double x;
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scanf("%lf", &x);
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printf("请输入n: ");
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int n;
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scanf("%d", &n);
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printf("P_n(x) = %lf\n", P(n, x));
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return 0;
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}
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```
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# P216 T14
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```C
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#include <stdio.h>
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double score[5][3];
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void Average_Student(void)
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{
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for (int i = 0; i < 5; ++i) {
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double avg = 0;
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for (int j = 0; j < 3; ++j) {
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avg += score[i][j];
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}
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avg /= 3;
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printf("第%d个学生的平均成绩是%f\n", i + 1, avg);
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}
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}
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void Average_Lesson(void)
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{
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for (int i = 0; i < 3; ++i) {
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double avg = 0;
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for (int j = 0; j < 5; ++j) {
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avg += score[j][i];
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}
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avg /= 5;
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printf("第%d门课程的平均成绩是%f\n", i + 1, avg);
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}
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}
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void Find_Max(void)
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{
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double max = score[0][0];
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int max_i = 0, max_j = 0;
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for (int i = 0; i < 5; ++i) {
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for (int j = 0; j < 3; ++j) {
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if (max < score[i][j]) {
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max = score[i][j];
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max_i = i;
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max_j = j;
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}
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}
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}
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printf("成绩最高的是第%d个学生的第%d门课程的成绩。\n", max_i + 1, max_j + 1);
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}
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void Calc_Var(void)
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{
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double sum_xi = 0;
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double sum_xi2 = 0;
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for (int i = 0; i < 3; ++i) {
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for (int j = 0; j < 5; ++j) {
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sum_xi2 += score[i][j];
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sum_xi2 += score[i][j] * score[i][j];
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}
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}
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double sigma = sum_xi2 / 15 - sum_xi * sum_xi / 225;
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printf("方差是%f\n", sigma);
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}
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int main()
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{
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for (int i = 0; i < 5; ++i) {
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for (int j = 0; j < 3; ++j) {
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printf("请输入第%d个学生的第%d门成绩：", i + 1, j + 1);
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scanf("%lf", &score[i][j]);
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}
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}
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Average_Student();
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Average_Lesson();
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Find_Max();
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Calc_Var();
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return 0;
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}
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```
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@ -6,39 +6,45 @@ date: 2020-10-30 09:39:53
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tags:
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---
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# 第六次作业
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- [题目](/~zhaozuohong/homework6/)
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- [答案](/~zhaozuohong/answer6/)
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- [讲解](/~zhaozuohong/resources/Experiment6.pdf)
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# 第一次大作业
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* [题目](/~zhaozuohong/big-homework1/)
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* [答案](/~zhaozuohong/big-answer1/)
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* [实验报告模板（ $\rm \LaTeX$ )](/~zhaozuohong/template1/)
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- [题目](/~zhaozuohong/big-homework1/)
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- [答案](/~zhaozuohong/big-answer1/)
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- [实验报告模板（ $\rm \LaTeX$ )](/~zhaozuohong/template1/)
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# 第五次作业
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* [题目](/~zhaozuohong/homework5/)
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* [答案](/~zhaozuohong/answer5/)
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* [讲解](/~zhaozuohong/resources/Experiment5.pdf)
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- [题目](/~zhaozuohong/homework5/)
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- [答案](/~zhaozuohong/answer5/)
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- [讲解](/~zhaozuohong/resources/Experiment5.pdf)
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# 第四次作业
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* [题目](/~zhaozuohong/homework4/)
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* [答案](/~zhaozuohong/answer4/)
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* [讲解](/~zhaozuohong/resources/Experiment4.pdf)
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- [题目](/~zhaozuohong/homework4/)
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- [答案](/~zhaozuohong/answer4/)
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- [讲解](/~zhaozuohong/resources/Experiment4.pdf)
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# 第三次作业
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* [题目](/~zhaozuohong/homework3/)
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* [答案](/~zhaozuohong/answer3)
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* [测试数据](/~zhaozuohong/test3)
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* [讲解](/~zhaozuohong/resources/Experiment3.pdf)
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- [题目](/~zhaozuohong/homework3/)
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- [答案](/~zhaozuohong/answer3)
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- [测试数据](/~zhaozuohong/test3)
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- [讲解](/~zhaozuohong/resources/Experiment3.pdf)
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# 第二次作业
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* [题目](/~zhaozuohong/homework2/)
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* [答案](/~zhaozuohong/answer2)
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* [讲解](/~zhaozuohong/resources/Experiment2.pptx)
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- [题目](/~zhaozuohong/homework2/)
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- [答案](/~zhaozuohong/answer2)
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- [讲解](/~zhaozuohong/resources/Experiment2.pptx)
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# 第一次作业
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* [题目](/~zhaozuohong/homework1/)
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* [答案](/~zhaozuohong/answer1)
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* [讲解](/~zhaozuohong/resources/Experiment1.pptx)
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- [题目](/~zhaozuohong/homework1/)
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- [答案](/~zhaozuohong/answer1)
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- [讲解](/~zhaozuohong/resources/Experiment1.pptx)
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49
source/_posts/homework6.md
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49
source/_posts/homework6.md
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@ -0,0 +1,49 @@
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---
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title: 第六次作业（题目）
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date: 2020-11-20 12:26:17
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tags:
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mathjax: true
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---
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# 冒泡排序
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对 10 个伪随机数冒泡排序，伪随机数产生方法可参考上面习题指导第 127 页，注意冒泡排序排好了要能提前退出。
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# 矩阵乘法
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实现两个矩阵相乘。
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# P166 T13
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编一程序，将两个字符串连接起来，不要用`strcat`函数。
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# P216 T13
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用递归方法求 $n$ 阶勒让德多项式的值，递归公式为：
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$$
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\begin{equation*}
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P_{n}(x) = \left \{
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\begin{array}{ll}
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1 & (n = 0) \\
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x & (n = 1) \\
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((2n-1) \times x P_{n-1}(x) - (n-1) \times P_{n-2}(x) ) / n & (n \geq 1)
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\end{array}
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\right .
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\end{equation*}
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$$
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# P216 T14
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输入 5 个学生 3 门课的成绩，分别用函数实现下列功能：
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1. 计算每个学生的平均分；
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2. 每门课的平均分；
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3. 找出所有 15 个中最高的所对应的学生和课程；
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4. 计算平均分方差。
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$$
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\begin{equation*}
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\sigma = \frac{1}{n} \sum x_i^2 - \left ( \frac{\sum x_i}{n} \right ) ^2
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\end{equation*}
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$$
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