C-将switch()与void()一起使用

Question

我想让我的代码询问用户，在void list((工作后，他/她是想使用void add(？

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语句，否则您的案例将通过进入下面的语句。

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

Answer 2

您的问题是的一个完美例子

为什么我应该始终启用编译器警告？

因为如果你在启用警告的情况下编译它，编译器会告诉你到底出了什么问题：

<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:
      |         ^~~~~~~

"跌倒"；意味着继续执行下一个案件。

Answer 3

Switch以贯穿机制而闻名。当发现特定情况时，执行附带标签中的语句，但执行将继续，直到到达[break；]语句或开关块的末尾。

在大多数情况下，逻辑设置将在单个事例块的末尾有break语句(尽管在许多情况下，使用fall-through算法(。您可以将[case1:]视为goto标签-程序跳到特定标签并从该点开始。

更重要的是，通常将单个事例中的语句放入{}块中是个好主意，尤其是当块中有局部变量声明时。