打破这个while循环

Question

我也从文本文件中读取：

George Washington, 2345678
John Adams, 3456789
Thomas Jefferson, 4567890
James Madison, 0987654
James Monroe, 9876543
John Quincy Adams, 8765432
Andrew Jackson, 7654321
Martin Van Buren, 6543210
William Henry Harrison, 5432109
John Tyler, 4321098

删除名称的功能有效，但是成功后，printf语句将继续在命令窗口中循环。 我尝试在循环的末尾使用break语句，但是这只会导致说找不到该名称。 有人可以提供任何见解吗？

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

//Creates node for holding student's information
struct node
{
    char name [50];
    int id;
    struct node *next;
}*head;

//Create Function Prototypes
void readDataFile ();
void insert(char *inName, char *inID);
void display(struct node *d);
int deleteID(int num);
void deleteName(char *delete_name);


//Main function
int main()
{
    //Declare variables
    int i, num, delete_id, id;
    char *name;
    char nameDelete [50];
    char nameInsert [50];
    struct node *n;

    //initialize link list
    head = NULL;

    //Read in file
    readDataFile();

    //Create list of operations utilized in program
    while (1)
    {
        printf("\nList Operations\n");
        printf("===============\n");
        printf("1.Insert\n");
        printf("2.Display\n");
        printf("3.Delete by ID\n");
        printf("4.Delete by Name\n");
        printf("5.Exit\n");
        printf("Enter your choice : ");

        if(scanf("%d", &i) <= 0)
        {
            printf("Enter only an Integer\n");
            exit(0);
        }
        else
        {
            switch(i)
            {
                case 1:
                    getchar();
                    printf("Enter the name to insert:");
                    scanf("%[^\n]s", nameInsert);
                    printf("\nEnter the ID associated with the name: ");
                    scanf("%d", &id);
                    break;
                case 2:
                    if (head == NULL)
                        printf("List is Empty\n");
                    else
                    {
                        printf("Elements in the list are:\n");
                    }
                    display(n);
                    break;
                case 3:
                    if(head == NULL)
                        printf("List is Empty\n");
                    else
                    {
                        printf("Enter the ID number to delete: ");
                        scanf("%d", &delete_id);
                    }

                    if(deleteID(delete_id))
                        printf("%d deleted successfully \n", delete_id);
                    else
                        printf("%d not found in the list\n", delete_id);
                    break;
                case 4:
                    getchar();
                    if(head == NULL)
                        printf("List is Empty\n");
                    else
                    {
                        printf("Enter name to delete: ");
                        scanf("%[^\n]s", nameDelete);
                        printf("Checking for name %s...\n", nameDelete);
                        printf("%s not found in the list\n", nameDelete);
                        deleteName(nameDelete);
                    }
                    break;
                case 5:
                    return 0;
                default:
                    printf("Invalid option\n");
            }
        }
    }
    return 0;
}

//Define the functions
//Function to delete by name
void deleteName(char *delete_name)
{
    //Create temporary and helper node
    struct node *temp, *helper;

    //Set temp equal to head
    temp = head;

    //Loop until the end of the list
    while(temp != NULL)
    {
        if(strcmp(temp->name, delete_name) == 0)
        {
            if(temp == head)
            {
                head = temp->next;
                free(temp);
                printf("Found %s!\n", delete_name);
                printf("%s deleted successfully\n", delete_name);
            }
            else
            {
                helper->next = temp->next;
                free(temp);
                printf("Found %s!\n", delete_name);
                printf("%s deleted successfully\n", delete_name);
            }
        }
        else
        {
            helper = temp;
            temp = temp->next;
        }
    }
break;
}

Answer 1

请学习如何制作MCVE（ 如何创建最小，完整和可验证的示例？ ）或SSCCE（ 简短，自包含，正确的示例 ）—两个名称和相同基本思想的链接。

这是从您的代码派生的MCVE。 我添加了丢失的break; 或return; 从deleteName()的循环开始。 我基本上完全重写了main() ，但它工作得很干净：

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

struct node
{
    char name[50];
    int id;
    struct node *next;
} *head;

void deleteName(char *delete_name);

int main(void)
{
    struct node *n;

    head = NULL;

    head = malloc(sizeof(*head));
    assert(head != 0);
    strcpy(head->name, "Abraham Lincoln");
    head->id = 1;
    head->next = 0;

    n = malloc(sizeof(*n));
    strcpy(n->name, "George Washington");
    n->id = 2;
    n->next = head;
    head = n;

    n = malloc(sizeof(*n));
    strcpy(n->name, "John Adams");
    n->id = 3;
    n->next = head;
    head = n;

    deleteName("George Washington");
    deleteName("John Adams");
    deleteName("Abraham Lincoln");

    return 0;
}

void deleteName(char *delete_name)
{
    struct node *temp, *helper = 0;

    temp = head;

    while (temp != NULL)
    {
        if (strcmp(temp->name, delete_name) == 0)
        {
            if (temp == head)
            {
                head = temp->next;
                free(temp);
                printf("Found %s!\n", delete_name);
                printf("%s deleted successfully\n", delete_name);
            }
            else
            {
                helper->next = temp->next;
                free(temp);
                printf("Found %s!\n", delete_name);
                printf("%s deleted successfully\n", delete_name);
            }
            return;  // The key change!
        }
        else
        {
            helper = temp;
            temp = temp->next;
        }
    }
}

可以在valgrind和Mac OS X 10.10.2（带有GCC 4.9.1）下正常运行。

Found George Washington!
George Washington deleted successfully
Found John Adams!
John Adams deleted successfully
Found Abraham Lincoln!
Abraham Lincoln deleted successfully

重要的是要学习如何在创建MCVE时残酷地删除不相关的代码。

Answer 2

break关键字将脱离最近的开关或循环。 因此，您可以尝试以下操作：

while(temp != NULL)
{
    if(strcmp(temp->name, delete_name) == 0)
    {
        if(temp == head)
        {
            head = temp->next;
            free(temp);
            printf("Found %s!\n", delete_name);
            printf("%s deleted successfully\n", delete_name);
            break;
        }
        else
        {
            helper->next = temp->next;
            free(temp);
            printf("Found %s!\n", delete_name);
            printf("%s deleted successfully\n", delete_name);
            break;
        }
    }
    else
    {
        helper = temp;
        temp = temp->next;
    }
}

另一种解决方案是在释放温度后将temp设置为NULL（无论如何这是一种好习惯，因此可能是另一个想法）

Answer 3

找到要删除的名称后，在if块的末尾添加return语句

void deleteName(char *delete_name)
{
    //Create temporary and helper node
    struct node *temp, *helper;

    //Set temp equal to head
    temp = head;

    //Loop until the end of the list
    while(temp != NULL)
    {
        if(strcmp(temp->name, delete_name) == 0)
        {
            if(temp == head)
            {
                head = temp->next;
                free(temp);
                printf("Found %s!\n", delete_name);
                printf("%s deleted successfully\n", delete_name);
            }
            else
            {
                helper->next = temp->next;
                free(temp);
                printf("Found %s!\n", delete_name);
                printf("%s deleted successfully\n", delete_name);
            }
            return; 
        }
        else
        {
            helper = temp;
            temp = temp->next;
        }
    }
}

另外，您还将计划指示该名称不是列表的一部分，而不是被查找和删除。 您可以更改modify函数，以使其在列表中找不到名称时返回错误代码，然后使用该函数指示该名称从未出现在列表中。

Answer 4

I did not really look at the delete() function,
however, the following code illustrates how the 
code should be formatted, etc.

notice the checking for input errors, which should always be performed
notice the separation of the struct definition from the struct declaration
notice the easy readability of the switch cases
    by incorporating some vertical white space
notice the simple comments after the closing braces
notice that no call to an action is performed if the linked list is empty



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

//define node for holding student's information
struct node
{
    char name [50];
    int id;
    struct node *next;
};

// create head pointer for linked list of student info
// and initialize
struct node *head = NULL;

// Function Prototypes
// note: if all these functions are only accessed within this file
//       then they should be declared with the 'static' modifier
void readDataFile (void);
void insert (char *inName, char *inID);
void display (struct node *d);
void deleteID (int delete_ID);
void deleteName (char *delete_name);


//Main function
int main()
{
    //Declare local variables
    // notice use of meaningful names
    // notice, for readability and documentation, 
    //         only one variable declared per line
    int i;  // receives user menu selection input
    int idDelete;
    int idInsert;
    char nameDelete [50];
    char nameInsert [50];
    // struct node *n; // unused variable
    int done = 0; // used to exit when user enters '5'



    //Read in file
    readDataFile();

    //Create list of operations utilized in program
    while (!done)
    {
        printf("\nList Operations\n");
        printf("===============\n");
        printf("1.Insert\n");
        printf("2.Display\n");
        printf("3.Delete by ID\n");
        printf("4.Delete by Name\n");
        printf("5.Exit\n");
        printf("Enter your choice : ");

        if( 1 != scanf("%d", &i) )
        { // then, scanf failed
            perror( "scanf for choice failed");
            exit( EXIT_FAILURE );
        }

        // implied else, scanf successful

        switch(i)
        {
            case 1:
                int ch;
                while(EOF != (ch = getchar()) && (ch != '\n'));

                printf("Enter the name to insert:");

                if( 1 != (scanf("%[^\n]s", nameInsert) ) )
                { // then scanf failed
                    perror( "scanf for new student name failed");
                    exit( EXIT_FAILURE );
                }

                // implied else, scanf successful

                printf("\nEnter the ID associated with the name: ");

                if( 1 != (scanf("%d", &idInsert) ) )
                { // then scanf failed
                    perror( "scanf for new student ID failed");
                    exit( EXIT_FAILURE );
                }

                // implied else, scanf successful

                insert( nameInsert, idInsert );
                break;

            case 2:
                if (head == NULL)
                    printf("List is Empty\n");
                else
                {
                    printf("Elements in the list are:\n");
                    display(n);
                } // end if
                break;

            case 3:
                if(head == NULL)
                    printf("List is Empty\n");
                else
                {
                    printf("Enter the ID number to delete: ");

                    if( 1 != (scanf("%d", &idDelete) ) )
                    { // then, scanf failed
                        perror( "scanf for ID to delete failed");
                        exit( EXIT_FAILURE );
                    } 

                    // implied else, scanf successful

                    deleteID(idDelete);
                } // end if
                break;

            case 4:
                int ch;
                while(EOF != (ch = getchar()) && (ch != '\n'));

                if(head == NULL)
                    printf("List is Empty\n");
                else
                {
                    printf("Enter name to delete: ");

                    if( 1 != (scanf("%[^\n]s", nameDelete) ) )
                    { // then, scanf failed
                        perror( "scanf for name to delete failed");
                        exit( EXIT_FAILURE );
                    }

                    // implied else, scanf successful

                    printf("Checking for name %s...\n", nameDelete);

                    deleteName(nameDelete);
                } // end if
                break;

            case 5:
                done = 1; // this will cause while() loop to exit
                break;

            default:
                printf("Invalid option\n");
                break;
        } // end switch
    } // end while
    return 0;
} // end of function: main