第三次作业题目和答案(未公布)

2020-10-30 13:59:49 +08:00 · 2020-10-30 13:59:49 +08:00 · b01ba87404
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+---
+title: 第二次作业（答案）
+mathjax: true
+date: 2020-10-30 10:35:37
+tags:
+---
+
+
+# P82-6
+
+```C
+#include <stdio.h>
+
+#define OFFSET 4
+
+int main()
+{
+    char c1 = 'C',
+         c2 = 'h',
+         c3 = 'i',
+         c4 = 'n',
+         c5 = 'a';
+
+    c1 += OFFSET;
+    c2 += OFFSET;
+    c3 += OFFSET;
+    c4 += OFFSET;
+    c5 += OFFSET;
+
+    /* 使用putchar()输出 */
+    putchar(c1);
+    putchar(c2);
+    putchar(c3);
+    putchar(c4);
+    putchar(c5);
+
+    /* 使用printf()输出 */
+
+    printf("%c%c%c%c%c", c1, c2, c3, c4, c5);
+
+    return 0;
+}
+```
+
+# P82-7
+
+圆半径 $r = 1.5$ ，圆柱高 $h = 3$ ，分别用变量`radius`和`height`存储。圆的周长 $P_{\mathrm{circle}} = 2 \pi r$ ，用变量`circle_perimeter`存储；圆的面积 $A_{\mathrm{circle}} = \pi r^{2}$ ，用变量`circle_area`存储；圆球表面积 $A_{\mathrm{sphere}} = 4 \pi r^{2}$ ，用变量`sphere_area`存储；圆球体积 $V_{\mathrm{ball}} = \frac{4}{3} \pi r^{3}$ ，用变量`ball_volume`存储；圆柱体积 $V_{\mathrm{cylinder}} = \pi r^{2} h$ ，用变量`cylinder_volume`存储。
+
+在这个程序中用到了`M_PI`，相关内容请见：[Math Constants](https://docs.microsoft.com/en-us/cpp/c-runtime-library/math-constants?view=vs-2019)，[19.1 Predefined Mathematical Constants](https://www.gnu.org/software/libc/manual/html_node/Mathematical-Constants.html)。
+
+```C
+#include <stdio.h>
+#include <stdlib.h>
+#define _USE_MATH_DEFINES
+#include <math.h>
+
+int main()
+{
+    printf("This program calculates the perimeter and area of the circle, ");
+    printf("the area and the volume of the ball, and the volume of the cylinder.\n");
+
+    double radius, height;
+    /* 检查用户输入是否合法 */
+    printf("Please input the radius: ");
+    if (scanf("%lf", &radius) != 1 || radius <= 0) {
+        printf("Invalid input!\n");
+        exit(EXIT_FAILURE);
+    }
+    printf("Please input the height: ");
+    if (scanf("%lf", &height) != 1 || height <= 0) {
+        printf("Invalid input!\n");
+        exit(EXIT_FAILURE);
+    }
+
+    double circle_perimeter = 2 * M_PI * radius;
+    printf("The perimeter of the circle is %.2f\n", circle_perimeter);
+
+    double circle_area = M_PI * radius * radius;
+    printf("The area of the circle is %.2f\n", circle_area);
+
+    double sphere_area = 4 * M_PI * radius * radius;
+    printf("The area of the sphere is %.2f\n", sphere_area);
+
+    double ball_volume = 4.0 / 3.0 * M_PI * radius * radius * radius;
+    printf("The volume of the ball is %.2f\n", ball_volume);
+
+    double cylinder_volume = M_PI * radius * radius * height;
+    printf("The volume of the cylinder is %.2f\n", cylinder_volume);
+
+    return 0;
+}
+```
+
+# P82-8
+
+```C
+#include <stdio.h>
+
+int main()
+{
+    char c1 = getchar();
+    char c2 = getchar();
+
+    putchar(c1);
+    putchar(c2);
+    printf("%c%c", c1, c2);
+
+    /* 打印ASCII码 */
+    printf("%d%d", c1, c2);
+
+    return 0;
+}
+```
+
+1. 二者皆可。
+2. 可以用`printf("%d", c1);`这种方式来输出它们的ASCII码。
+3. 不可以。两者占用的内存空间不同，表示的数的范围不同。`char`类型是不是有符号类型，视实现而定。
+
+# 温度转换
+
+```C
+#include <stdio.h>
+#include <stdlib.h>
+
+int main()
+{
+    printf("Please input the temperature (in fahrenheit): ");
+
+    double degree_f;
+    if (scanf("%lf", &degree_f) != 1) {
+        printf("Invalid input!\n");
+        exit(EXIT_FAILURE);
+    }
+
+    double degree_c = (degree_f - 32.0) * 5.0 / 9.0;
+
+    printf("%.1f degree fahrenheit equals to %.1f degree celsius.\n", degree_f, degree_c);
+
+    return 0;
+}
+```