C - 将 switch() 与 void() 一起使用

Question

我希望我的代码询问用户 he/she 是否要使用 void add() 添加文本或使用 删除一行void delrow() after void list() 有效，但代码在询问后同时执行 add() 和 delrow() 。我应该如何使用switch语句？

谢谢。

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

#define FILENAME_SIZE 128
#define MAX_LINE 2048


void list(){                    // Printing the list.
char filename[100];
printf("\n*** TODO List ***\n ");

FILE *fptr ;
printf("\nPlease enter the file name with its extension: ");
    scanf("%s", filename);
    
    fptr = fopen(filename, "r");

char ch[100];                   // Character limit.
while(fgets(ch,sizeof(ch),fptr)){
  printf("%s",ch);
}
}

void add(){                     // Adding text to list.
char todo[150];                 // Character limit.
char filename[100];
FILE *fptr ;
printf("\n***TODO List - Add ToDo***\n ");
printf("\nPlease enter the file name with its extension:");
    scanf("%s", filename);
    
    fptr = fopen(filename, "a");

printf("\nEnter todo:");          // Getting the text.
scanf("%s",todo);

fprintf(fptr,"\n%s",todo);       // Importing the text.

}

void delrow(){
  
  printf("\n***TODO List - Delete Rows***\n ");
  FILE *fileptr1, *fileptr2;

        char filename[40];
        // File name limit
        char ch;
        int delete_line, temp = 1;

        printf("\nPlease enter the file name with its extension: ");
        scanf("%s", filename);

        //open file in read mode
        fileptr1 = fopen(filename, "r");
        ch = getc(fileptr1);

       while (ch != EOF)
        {
            printf("%c", ch);
            ch = getc(fileptr1);
        }

        //rewind
        rewind(fileptr1);

        printf(" \n Please enter line number of the line to be deleted:");
        scanf("%d", &delete_line);

        //open new file in write mode
        fileptr2 = fopen("temp", "w");

        ch = getc(fileptr1);

        while (ch != EOF)
        {
            ch = getc(fileptr1);
            if (ch == '\n')
                temp++;
                //except the line to be deleted
                if (temp != delete_line)
                {
                    //copy all lines in file replica.c
                    putc(ch, fileptr2);
                }
        }

        fclose(fileptr1);
        fclose(fileptr2);
        remove(filename);

        //rename the file temporary to original name

        rename("temp", filename);

        printf("\n The contents of file after being modified are as follows:\n");

        fileptr1 = fopen(filename, "r");

        ch = getc(fileptr1);

        while (ch != EOF)

        {

            printf("%c", ch);

            ch = getc(fileptr1);

        }

        fclose(fileptr1);
        
}

int main(void) {

int choice=0;
list();
printf("\nPlease state if you want to add todo or delete an existing todo (1:add 2:delete): ");
scanf("%d",&choice);
switch(choice){
case 1:
add();
case 2:
delrow();
default:
printf("\nUnacceptable choice.");
}
  return 0;
}

Answer 1

您必须添加 break 陈述，否则您的案例将落入到下面的案例中。

switch (choice) {
    case 1:
        add();
        break;
    case 2:
        delrow();
        break;
    default:
        printf("\nUnacceptable choice.");
}

Answer 2

Switch 以掉落机制而闻名。当发现特定情况时，将执行来自随附标签的语句，但会继续执行直到到达 [break;] 语句或开关块的末尾。

在大多数情况下，逻辑设置是在单个 case 块的末尾添加 break 语句（尽管在许多情况下，算法的使用会失败）。您可以将 [ case 1: ] 视为 goto label - 程序跳转到特定标签并从该点开始。

更重要的是，将单个 case 中的语句放入 { } 块通常是个好主意，尤其是在块内有局部变量声明的情况下。

Answer 3

你的问题是一个完美的例子：

因为如果您 compile it with warnings enabled，编译器会准确地告诉您哪里出了问题：

<source>: In function 'int main()':
<source>:116:16: warning: this statement may fall through [-Wimplicit-fallthrough=]
  116 |             add();
      |             ~~~^~
<source>:117:9: note: here
  117 |         case 2:
      |         ^~~~
<source>:118:19: warning: this statement may fall through [-Wimplicit-fallthrough=]
  118 |             delrow();
      |             ~~~~~~^~
<source>:119:9: note: here
  119 |         default:
      |         ^~~~~~~

“fall through”表示继续执行下一个case。

C - 将 switch() 与 void() 一起使用

C - Using switch() with void()

c

void

switch-statement