请问这个程序为什么结果是0.#include <stdio.h> #include <stdlib.h> float compute(float x,char oper,float y) { float z; //char oper; switch (oper) { case '+': z = x + y; case '-': z = x - y; case '*': z = x * y; case '/': z = x / y; } return z; } int main(int argc, char *argv[]) { float a,b; char oper; scanf("%f%c%f",&a,&oper,&b); printf("=%f\n",compute(a,oper,b)); return 0; }

这个程序结果为0是因为在switch语句中，每个case后面都没有break语句，导致程序会顺序执行下去，直到遇到return语句为止。当输入运算符为'+','-','*','/'时，程序会进入相应的case分支中执行对应的运算，但是由于没有break语句，程序会继续执行下去，最终返回的值是默认的0。如果要修复这个问题，需要在每个case分支中添加break语句。

相关问题

编写代码实现一个自定义浮点数，符合IEE754规范，共16位，其中exp占6bits, frac占 9bits.（1）输入一个16进制数，输出这个16进制的二进制表达，得到符合这个自定义浮点数的小数； （2）输出十六进制串的二进制表达(Transfer.c) (3) 按照IEEE 754浮点数标准设计16bit浮点计算（考虑规范数，非规范，和特殊值）(Compute.c) (4)输出16bits 设计规则下，二进制字符串 （5）遍写makefile运行 (main.c Transfer.c Compute.c)

非常感谢您的提问，以下是对应的代码实现：

1. 自定义浮点数的实现

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef union {
    float f;
    struct {
        unsigned int mantissa : 9;
        unsigned int exponent : 6;
        unsigned int sign : 1;
    } parts;
} custom_float;

int main() {
    // 输入十六进制数
    char hex_str[5];
    printf("请输入一个16进制数: ");
    scanf("%s", hex_str);

    // 转换为二进制字符串
    int num = (int) strtol(hex_str, NULL, 16);
    char binary_str[17];
    for (int i = 15; i >= 0; i--) {
        binary_str[15 - i] = (num & (1 << i)) ? '1' : '0';
    }
    binary_str[16] = '\0';

    // 计算指数和尾数
    custom_float cf;
    cf.parts.sign = binary_str[0] - '0';
    cf.parts.exponent = 0;
    for (int i = 1; i <= 6; i++) {
        cf.parts.exponent = cf.parts.exponent * 2 + (binary_str[i] - '0');
    }
    cf.parts.mantissa = 0;
    for (int i = 7; i <= 15; i++) {
        cf.parts.mantissa = cf.parts.mantissa * 2 + (binary_str[i] - '0');
    }

    // 输出结果
    printf("输入的二进制表达: %s\n", binary_str);
    printf("对应的自定义浮点数: %f\n", cf.f);

    return 0;
}

2. 十六进制串的二进制表达

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

int main() {
    // 输入十六进制数
    char hex_str[5];
    printf("请输入一个16进制数: ");
    scanf("%s", hex_str);

    // 转换为二进制字符串
    int num = (int) strtol(hex_str, NULL, 16);
    char binary_str[17];
    for (int i = 15; i >= 0; i--) {
        binary_str[15 - i] = (num & (1 << i)) ? '1' : '0';
    }
    binary_str[16] = '\0';

    // 输出结果
    printf("输入的十六进制串: %s\n", hex_str);
    printf("对应的二进制表达: %s\n", binary_str);

    return 0;
}

3. 自定义浮点数的计算

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

typedef union {
    float f;
    struct {
        unsigned int mantissa : 9;
        unsigned int exponent : 6;
        unsigned int sign : 1;
    } parts;
} custom_float;

custom_float add(custom_float a, custom_float b) {
    custom_float result;
    // 先判断特殊值
    if (a.parts.exponent == 0b111111 || b.parts.exponent == 0b111111) {
        // NaN或Infinity
        result.parts.sign = 0;
        result.parts.exponent = 0b111111;
        result.parts.mantissa = 1;
    } else if (a.parts.exponent == 0 && a.parts.mantissa == 0) {
        // 零值
        result = b;
    } else if (b.parts.exponent == 0 && b.parts.mantissa == 0) {
        // 零值
        result = a;
    } else {
        // 规范数相加
        // 先计算两个数的指数之差
        int exp_diff = a.parts.exponent - b.parts.exponent;
        if (exp_diff < 0) {
            // 交换a和b，使得a的指数大于等于b的指数
            custom_float temp = a;
            a = b;
            b = temp;
            exp_diff = -exp_diff;
        }
        // 将b的尾数左移exp_diff位，使得两个数的小数点对齐
        b.parts.mantissa <<= exp_diff;
        // 相加
        result.parts.sign = a.parts.sign;
        result.parts.exponent = a.parts.exponent;
        result.parts.mantissa = a.parts.mantissa + b.parts.mantissa;
        // 如果相加后的结果超过了9位，则需要右移尾数并增加指数
        if (result.parts.mantissa & (1 << 9)) {
            result.parts.mantissa >>= 1;
            result.parts.exponent++;
        }
    }
    return result;
}

int main() {
    // 输入两个自定义浮点数
    custom_float a, b;
    printf("请输入第一个自定义浮点数: ");
    scanf("%f", &a.f);
    printf("请输入第二个自定义浮点数: ");
    scanf("%f", &b.f);

    // 计算结果
    custom_float result = add(a, b);

    // 输出结果
    printf("计算结果的二进制表达: %c%d%c\n",
           result.parts.sign ? '-' : '+',
           result.parts.exponent,
           result.parts.mantissa ? '.' : ' ');
    for (int i = 8; i >= 0; i--) {
        printf("%d", (result.parts.mantissa >> i) & 1);
    }
    printf("\n");

    return 0;
}

4. 输出16bits 设计规则下，二进制字符串

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef union {
    float f;
    struct {
        unsigned int mantissa : 9;
        unsigned int exponent : 6;
        unsigned int sign : 1;
    } parts;
} custom_float;

int main() {
    // 输入一个自定义浮点数
    custom_float cf;
    printf("请输入一个自定义浮点数: ");
    scanf("%f", &cf.f);

    // 计算指数和尾数的二进制表达
    char exponent_binary_str[7];
    for (int i = 5; i >= 0; i--) {
        exponent_binary_str[5 - i] = (cf.parts.exponent & (1 << i)) ? '1' : '0';
    }
    exponent_binary_str[6] = '\0';
    char mantissa_binary_str[10];
    for (int i = 8; i >= 0; i--) {
        mantissa_binary_str[8 - i] = (cf.parts.mantissa & (1 << i)) ? '1' : '0';
    }
    mantissa_binary_str[9] = '\0';

    // 计算符号位
    char sign_str[2];
    sign_str[0] = cf.parts.sign ? '1' : '0';
    sign_str[1] = '\0';

    // 拼接成16位二进制字符串
    char binary_str[17];
    strncpy(binary_str, sign_str, sizeof(sign_str));
    strncat(binary_str, exponent_binary_str, sizeof(exponent_binary_str));
    strncat(binary_str, mantissa_binary_str, sizeof(mantissa_binary_str));

    // 输出结果
    printf("输入的自定义浮点数: %f\n", cf.f);
    printf("对应的二进制表达: %s\n", binary_str);

    return 0;
}

5. makefile文件

CC = gcc
CFLAGS = -Wall

all: main

main: main.c Transfer.o Compute.o
	$(CC) $(CFLAGS) -o $@ $^

Transfer.o: Transfer.c
	$(CC) $(CFLAGS) -c $<

Compute.o: Compute.c
	$(CC) $(CFLAGS) -c $<

clean:
	rm -f main Transfer.o Compute.o

应用《C语言程序设计》和《数据结构》课程的内容，编写一个完整的学生成绩管理系统程序，实现以下题目的要求： 1.学生信息包括学号、姓名、3 门考试成绩 2.学生成绩录入功能(成绩信息用文件保存) 3.统计所有学生的总分及平均分 4.统计所有课程的平均分 5.按平均分进行排序 6.输入一个学生学号输出其各科成绩及平均成绩 7.修改、删除学生信息

好的，这是一个比较复杂的程序，需要涉及到文件的读写、数据结构的使用等内容。下面是一个简单的示例程序，可以供您参考：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_NAME_LEN 20
#define MAX_STUDENTS 100

typedef struct {
    int id;
    char name[MAX_NAME_LEN];
    int scores[3];
    float total_score;
    float avg_score;
} Student;

int read_students(Student students[]) {
    FILE *fp;
    int i = 0;
    char filename[] = "students.dat";
    fp = fopen(filename, "rb");
    if (fp == NULL) {
        printf("Cannot open file %s\n", filename);
        return 0;
    }
    while (fread(&students[i], sizeof(Student), 1, fp) == 1) {
        i++;
    }
    fclose(fp);
    return i;
}

void write_students(Student students[], int num_students) {
    FILE *fp;
    char filename[] = "students.dat";
    fp = fopen(filename, "wb");
    if (fp == NULL) {
        printf("Cannot open file %s\n", filename);
        return;
    }
    fwrite(students, sizeof(Student), num_students, fp);
    fclose(fp);
}

void add_student(Student students[], int *num_students) {
    if (*num_students >= MAX_STUDENTS) {
        printf("Cannot add more students\n");
        return;
    }
    printf("Enter student ID: ");
    scanf("%d", &students[*num_students].id);
    printf("Enter student name: ");
    scanf("%s", students[*num_students].name);
    printf("Enter scores for three exams:\n");
    scanf("%d %d %d", &students[*num_students].scores[0], &students[*num_students].scores[1], &students[*num_students].scores[2]);
    students[*num_students].total_score = students[*num_students].scores[0] + students[*num_students].scores[1] + students[*num_students].scores[2];
    students[*num_students].avg_score = students[*num_students].total_score / 3.0;
    (*num_students)++;
    write_students(students, *num_students);
}

void print_student(Student student) {
    printf("%d\t%s\t%d\t%d\t%d\t%.2f\t%.2f\n", student.id, student.name, student.scores[0], student.scores[1], student.scores[2], student.total_score, student.avg_score);
}

void print_all_students(Student students[], int num_students) {
    int i;
    printf("ID\tName\tExam 1\tExam 2\tExam 3\tTotal\tAverage\n");
    for (i = 0; i < num_students; i++) {
        print_student(students[i]);
    }
}

void compute_scores(Student students[], int num_students) {
    int i, j;
    float exam_totals[3] = {0.0};
    float class_total = 0.0;
    for (i = 0; i < num_students; i++) {
        class_total += students[i].total_score;
        for (j = 0; j < 3; j++) {
            exam_totals[j] += students[i].scores[j];
        }
    }
    printf("Class average:\n");
    for (j = 0; j < 3; j++) {
        printf("Exam %d: %.2f\n", j+1, exam_totals[j] / num_students);
    }
    printf("Total: %.2f\n", class_total / num_students);
}

void sort_by_average(Student students[], int num_students) {
    int i, j;
    Student temp;
    for (i = 0; i < num_students-1; i++) {
        for (j = i+1; j < num_students; j++) {
            if (students[i].avg_score < students[j].avg_score) {
                temp = students[i];
                students[i] = students[j];
                students[j] = temp;
            }
        }
    }
}

void find_student(Student students[], int num_students) {
    int id, i;
    printf("Enter student ID: ");
    scanf("%d", &id);
    for (i = 0; i < num_students; i++) {
        if (students[i].id == id) {
            printf("ID\tName\tExam 1\tExam 2\tExam 3\tTotal\tAverage\n");
            print_student(students[i]);
            return;
        }
    }
    printf("No student with ID %d found\n", id);
}

void modify_student(Student students[], int num_students) {
    int id, i;
    printf("Enter student ID: ");
    scanf("%d", &id);
    for (i = 0; i < num_students; i++) {
        if (students[i].id == id) {
            printf("Enter new scores for three exams:\n");
            scanf("%d %d %d", &students[i].scores[0], &students[i].scores[1], &students[i].scores[2]);
            students[i].total_score = students[i].scores[0] + students[i].scores[1] + students[i].scores[2];
            students[i].avg_score = students[i].total_score / 3.0;
            write_students(students, num_students);
            printf("Student %d updated\n", id);
            return;
        }
    }
    printf("No student with ID %d found\n", id);
}

void delete_student(Student students[], int *num_students) {
    int id, i, j;
    printf("Enter student ID: ");
    scanf("%d", &id);
    for (i = 0; i < *num_students; i++) {
        if (students[i].id == id) {
            for (j = i; j < *num_students-1; j++) {
                students[j] = students[j+1];
            }
            (*num_students)--;
            write_students(students, *num_students);
            printf("Student %d deleted\n", id);
            return;
        }
    }
    printf("No student with ID %d found\n", id);
}

int main() {
    Student students[MAX_STUDENTS];
    int num_students = 0;
    int choice;
    num_students = read_students(students);
    while (1) {
        printf("Choose an option:\n");
        printf("1. Add a student\n");
        printf("2. Print all students\n");
        printf("3. Compute scores\n");
        printf("4. Sort by average\n");
        printf("5. Find a student\n");
        printf("6. Modify a student\n");
        printf("7. Delete a student\n");
        printf("8. Exit\n");
        scanf("%d", &choice);
        switch (choice) {
            case 1:
                add_student(students, &num_students);
                break;
            case 2:
                print_all_students(students, num_students);
                break;
            case 3:
                compute_scores(students, num_students);
                break;
            case 4:
                sort_by_average(students, num_students);
                print_all_students(students, num_students);
                break;
            case 5:
                find_student(students, num_students);
                break;
            case 6:
                modify_student(students, num_students);
                break;
            case 7:
                delete_student(students, &num_students);
                break;
            case 8:
                write_students(students, num_students);
                exit(0);
            default:
                printf("Invalid choice\n");
                break;
        }
    }
    return 0;
}

这段代码实现了一个简单的学生成绩管理系统，包含了添加学生、打印所有学生、统计所有学生的总分及平均分、按平均分进行排序、输入一个学生学号输出其各科成绩及平均成绩、修改、删除学生信息等功能。代码中使用了结构体来存储学生信息，使用了文件来保存数据，并且使用了一些简单的数据结构和算法来实现排序等功能。