System.out.printf("%.1f ", scores[i]);和System.out.printf("%.1f "+scores[i]);写法都正确吗

`System.out.printf("%.1f ", scores[i])` 和 `System.out.printf("%.1f "+scores[i])` 这两个写法从语法角度来看，并不完全正确。`System.out.printf()` 是 Java 中用于格式化输出的一个函数，它接受一个格式字符串作为第一个参数，然后跟随着一些占位符。

在这个例子中，`%.1f` 是一个浮点数的格式控制符，表示保留一位小数。空格 (` `) 是用来指定输出后跟一个空格。所以正确的方式来输出分数并带有一个空格应该是在格式字符串后面直接加空格，像这样：

System.out.printf("%.1f ", scores[i]);

然而，`System.out.printf("%.1f "+scores[i])` 中的第二个 "+" 是错误的，因为它试图将一个字符串 "+" 和分数连接起来，而不是作为一个占位符。如果想要在打印每个分数后立即跟一个空格，应该直接在格式字符串中添加空格，不需要额外的操作符。

正确的写法只有一个空格：

System.out.printf("%.1f ", scores[i]);

相关问题

Write the C program according to the following menu interface - student information management system; 1）Enter student information: first enter the number of students, and then enter the corresponding information into the array according to the number of students; 2）Student information includes student number, name, gender, three course scores and total scores; Student number, name, gender and grades of three courses need to be entered from the keyboard, and the total score is calculated by the program, not by the user himself. 3）The display results (student information) shall be displayed in the form of list, paying attention to aesthetics; 4）Necessary fault tolerance measures shall be taken. For example, the score of each subject shall be between 0-100. If the input is wrong, the user shall be prompted to re-enter.

Sure, here's a C program that implements the student information management system with the menu interface you specified:

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

#define MAX_STUDENTS 100

struct student {
    int id;
    char name[50];
    char gender[10];
    int scores[3];
    int total_score;
};

int read_int() {
    int n;
    while (scanf("%d", &n) != 1) {
        printf("Invalid input, please enter an integer: ");
        scanf("%*[^\n]");
    }
    scanf("%*[^\n]");
    scanf("%*c");
    return n;
}

void read_string(char* str, int max_len) {
    char* p = fgets(str, max_len, stdin);
    if (p == NULL) {
        printf("Invalid input, please try again: ");
        read_string(str, max_len);
    } else {
        int len = strlen(str);
        if (len > 0 && str[len - 1] == '\n') {
            str[len - 1] = '\0';
        }
    }
}

void enter_student_info(struct student* students, int num_students) {
    printf("Enter student information:\n");
    for (int i = 0; i < num_students; i++) {
        printf("Student %d:\n", i + 1);
        printf("  ID: ");
        students[i].id = read_int();
        printf("  Name: ");
        read_string(students[i].name, sizeof(students[i].name));
        printf("  Gender: ");
        read_string(students[i].gender, sizeof(students[i].gender));
        for (int j = 0; j < 3; j++) {
            printf("  Score in course %d: ", j + 1);
            students[i].scores[j] = read_int();
            while (students[i].scores[j] < 0 || students[i].scores[j] > 100) {
                printf("Invalid score, please enter a score between 0 and 100: ");
                students[i].scores[j] = read_int();
            }
        }
        students[i].total_score = students[i].scores[0] + students[i].scores[1] + students[i].scores[2];
    }
}

void display_student_info(const struct student* students, int num_students) {
    printf("ID    Name               Gender Course 1 Course 2 Course 3 Total\n");
    printf("----------------------------------------------------------------\n");
    for (int i = 0; i < num_students; i++) {
        printf("%-5d%-19s%-8s%-9d%-9d%-9d%-5d\n", students[i].id, students[i].name, students[i].gender, students[i].scores[0], students[i].scores[1], students[i].scores[2], students[i].total_score);
    }
}

int main() {
    struct student students[MAX_STUDENTS];
    int num_students = 0;
    while (1) {
        printf("Student information management system:\n");
        printf("1) Enter student information\n");
        printf("2) Display student information\n");
        printf("3) Exit\n");
        printf("Please enter a choice (1-3): ");
        int choice = read_int();
        switch (choice) {
            case 1:
                printf("Enter the number of students: ");
                num_students = read_int();
                while (num_students < 1 || num_students > MAX_STUDENTS) {
                    printf("Invalid number of students, please enter a number between 1 and %d: ", MAX_STUDENTS);
                    num_students = read_int();
                }
                enter_student_info(students, num_students);
                printf("Student information entered successfully.\n");
                break;
            case 2:
                if (num_students == 0) {
                    printf("No student information entered yet.\n");
                } else {
                    display_student_info(students, num_students);
                }
                break;
            case 3:
                printf("Exiting...\n");
                exit(0);
            default:
                printf("Invalid choice, please enter a number between 1 and 3.\n");
        }
    }
    return 0;
}

This program uses a struct to store the information of each student, and an array of structs to store the information of all students. The `read_int()` function and `read_string()` function are used for input validation, to make sure that the user enters valid integers and strings. The `enter_student_info()` function prompts the user to enter the information of each student, validates the scores, and calculates the total score. The `display_student_info()` function displays the student information in a formatted table. The `main()` function implements the menu interface and calls the other functions based on the user's choice. The program also includes some fault tolerance measures, such as checking the number of students entered, checking the validity of the scores, and handling invalid input.

java编写1、题目描述：某班有30名学生，每个学生有学号、姓名和4门成绩（学生信息随机产生，存入一个对象数组），现新转来一名学生，请输入这位学生的学号、姓名和成绩（四门课的成绩小于100分，从键盘输入，以空格为区分），然后显示这名学生平均分、最高分，全班的最高平均分学生信息、新同学在班级中的成绩水平，可能的结果如下所示：例1:请输入学生姓名: jack请输入学生学号: 13201109请输入四门课的成绩，以空格分隔: 89 78 94 0jack(ID: 13201109) 平均分 66.50 最高分 94.00rose (ID:13201104) 的最高平均分 90.12 最高分 100.00jack的平均成绩低于全班的平均分例2请输入学生姓名: jack请输入学生学号: 13201109请输入四门课的成绩，以空格分隔: 100 85 65 85jack(ID: 13201109) 平均分 72.38 最高分 100.00rose (ID:13201104) 的最高平均分 90.12 最高分 100.00jack的平均成绩高于全班的平均分例3请输入学生姓名: jack请输入学生学号: 13201109请输入四门课的成绩，以空格分隔: 110 845 100000 100课程成绩不能高于100分！！例4请输入学生姓名: jack请输入学生学号: 13201109请输入四门课的成绩，以空格分隔: 100 100 100 100jack(ID: 13201109) 平均分 100.00 最高分 100.00jack现在是班上成绩最好的学生了jack的平均成绩高于全班的平均分

下面是Java代码实现：

import java.util.Scanner;

public class Student {
private String name; // 姓名
private String ID; // 学号
private int[] scores; // 四门成绩

public Student(String name, String ID, int[] scores) {
this.name = name;
this.ID = ID;
this.scores = scores;
}

public String getName() {
return name;
}

public String getID() {
return ID;
}

public int[] getScores() {
return scores;
}

public double getAverageScore() {
int sum = 0;
for (int score : scores) {
sum += score;
}
return (double) sum / scores.length;
}

public int getHighestScore() {
int max = scores[0];
for (int score : scores) {
if (score > max) {
max = score;
}
}
return max;
}

public static Student[] generateStudents(int num) {
String[] names = {"jack", "rose", "tom", "mary", "jim", "lucy", "bob", "kate", "david", "susan"};
Student[] students = new Student[num];
for (int i = 0; i < num; i++) {
String name = names[(int) (Math.random() * names.length)];
String ID = "13201" + (int) (Math.random() * 10000);
int[] scores = new int[4];
for (int j = 0; j < 4; j++) {
scores[j] = (int) (Math.random() * 100);
}
students[i] = new Student(name, ID, scores);
}
return students;
}

public static Student findHighestAverageScoreStudent(Student[] students) {
Student highestAverageScoreStudent = students[0];
double highestAverageScore = students[0].getAverageScore();
for (int i = 1; i < students.length; i++) {
double averageScore = students[i].getAverageScore();
if (averageScore > highestAverageScore) {
highestAverageScore = averageScore;
highestAverageScoreStudent = students[i];
}
}
return highestAverageScoreStudent;
}

public static boolean checkScoresInRange(int[] scores) {
for (int score : scores) {
if (score < 0 || score > 100) {
return false;
}
}
return true;
}

public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);

// 生成班级学生信息
Student[] students = generateStudents(30);

// 输入新转来的学生信息
System.out.print("请输入新转来的学生姓名：");
String name = scanner.next();
System.out.print("请输入新转来的学生学号：");
String ID = scanner.next();
int[] scores = new int[4];
System.out.print("请输入新转来的学生四门课成绩，以空格分隔：");
scores[0] = scanner.nextInt();
scores[1] = scanner.nextInt();
scores[2] = scanner.nextInt();
scores[3] = scanner.nextInt();
while (!checkScoresInRange(scores)) {
System.out.print("课程成绩不能高于100分，请重新输入新转来的学生四门课成绩：");
scores[0] = scanner.nextInt();
scores[1] = scanner.nextInt();
scores[2] = scanner.nextInt();
scores[3] = scanner.nextInt();
}
Student newStudent = new Student(name, ID, scores);

// 计算并显示新学生的平均分和最高分
double newStudentAverageScore = newStudent.getAverageScore();
int newStudentHighestScore = newStudent.getHighestScore();
System.out.printf("%s(ID: %s) 平均分 %.2f 最高分 %.2f\n", newStudent.getName(), newStudent.getID(),
newStudentAverageScore, (double) newStudentHighestScore);

// 计算并显示全班最高平均分学生信息
Student highestAverageScoreStudent = findHighestAverageScoreStudent(students);
double highestAverageScore = highestAverageScoreStudent.getAverageScore();
int highestAverageScoreStudentHighestScore = highestAverageScoreStudent.getHighestScore();
System.out.printf("%s(ID:%s) 的最高平均分 %.2f 最高分 %.2f\n", highestAverageScoreStudent.getName(),
highestAverageScoreStudent.getID(), highestAverageScore, (double) highestAverageScoreStudentHighestScore);

// 比较新学生与全班平均分的大小
double classAverageScore = 0;
for (Student student : students) {
classAverageScore += student.getAverageScore();
}
classAverageScore /= students.length;
if (newStudentAverageScore > classAverageScore) {
System.out.println(newStudent.getName() + "的平均成绩高于全班的平均分");
} else if (newStudentAverageScore < classAverageScore) {
System.out.println(newStudent.getName() + "的平均成绩低于全班的平均分");
} else {
System.out.println(newStudent.getName() + "的平均成绩与全班平均分相等");
}
}
}