C - Using switch() with void()-CodePudding

I want my code to ask user if he/she wants to either add text by using void add() or delete a line by using void delrow() after void list() works, but the code performs both add() and delrow() after asking it. How should I use the switch statement?

Thanks.

#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;
}

CodePudding user response：

You must add break statements or your cases will fall through to the one below.

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

CodePudding user response：

Your question is a perfect example of:

Why should I always enable compiler warnings?

because if you were to compile it with warnings enabled, the compiler would tell you exactly what's wrong:

<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" means continue execution of the next case.

CodePudding user response：

Switch is well known for fall through mechanism. When particular case is found, statement from accompanying label is executed, but execution continues until [break;] statement or end of the switch block is reached.

In most of the cases, the logical setup would be to have break statement at the end of the single case block (although, there is a number of situations where one uses fall through in algorithm). You can consider [ case 1: ] as goto label - program jumps to the particular label and goes from that point onwards.

Even more, it is, usually, good idea to have statements from single case put into { } block, especially if there are local variables declaration within the block.