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cstringatoi

cannot convert char to int when using atoi

I am creating a function findBookID. When I try to convert the book id into integer it shows me an error.
can anyone provide me a solution to solve this? Regards.
The error is last in the post.

strncpy(bookId, source + pos_text + 1, len_text - pos_text);
int i = atoi(bookId);       //atoi converts the string to integer
if (id == i)
{
  return true;
}

Here is how i declare the function

bool findBookId(char source[], int id)
{
    char input[10] = "Book ID: ";
    char bookId[5];
    int int_id = 0;
    int pos_search = 0;
    int pos_text = 0;
    int len_search = 10;
    size_t len_text = strlen(source);
    if (len_search < len_text)
    {

        for (pos_text = 0; pos_text < len_search - 1; ++pos_text)
        {
            if (source[pos_text] == input[pos_search])
            {

                ++pos_search;
                if (pos_search == len_search - 1)
                {
                    // match

                    strncpy(bookId, source + pos_text + 1, len_text - pos_text);
                    int i = atoi(bookId);       //atoi converts the string to integer
                    if (id == i){
                        return true;
                    }


                }
            }
            else
            {
                pos_text -= pos_search;
                pos_search = 0;
            }
        }
    }
    return false;
}

Full coding for Reference:https://drive.google.com/open?id=1zHc_26kFPVHs0b99-gkX1hdQ3AYykCPL9KegI5QobdY

This is the error message: function call is not allow a constant expression enter image description here

Solution

  • A main problem of many IDEs is the lack of legible warnings. If I try to compile your code (Google is not good for code, your entry suffers from C&P errors) with GCC I get the following errors:

    $ gcc -g3 -std=c11 -W -Wall bookid.c  -o bookid
bookid.c: In function ‘addbook’:
bookid.c:106:3: warning: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[50]’ [-Wformat=]
   scanf("%s", &book.name);
   ^
bookid.c: In function ‘editbook’:
bookid.c:180:3: warning: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[50]’ [-Wformat=]
   scanf("%s", &book.name);
   ^
bookid.c: In function ‘deletebook’:
bookid.c:270:5: warning: format ‘%c’ expects a matching ‘int’ argument [-Wformat=]
     printf("%c, c");
     ^
bookid.c: In function ‘findBookId’:
bookid.c:469:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if (len_search < len_text) {
                  ^
bookid.c:464:7: warning: unused variable ‘int_id’ [-Wunused-variable]
   int int_id = 0;
       ^
/tmp/ccijPXxB.o: In function `main':
bookid.c:85: undefined reference to `search'
collect2: error: ld returned 1 exit status

    For the first errors change scanf("%s", &book.name); to scanf("%s", book.name);

    The typo printf("%c, c"); should be printf("%c", c);

    comparison between signed and unsigned integer can be ignored for now (but should be repaired later, of course!)

    If you do not need a variable, comment it out.

    The last one, the fatal error, has its cause with a function named Search() called by the name of search(). C is case-sensitive.

    Case sensitivity also plays a large role with the broken search: you safe the file booklist.txt but want to read from BookList.txt (does that still work in Windows?).