Can anyone tell me why I am getting an error
Code:// isbnreader123.cpp : main project file. #include "stdafx.h" //visual studio #include <stdio.h> // printf scanf #include <ctype.h> // tolower #include <string.h> // strlen #include <stdlib.h> // isdigit atoi #include <process.h> // system() void hello(void); //program to welcome user char is_valid (char vaild_y_n); // checks for yes or no to continue program int is_valid_isbn (char isbn[]); //function to check for non numeric input within ISBN int check_digit_calc(void); //calculates check digit char isbn[13]; //array for ISBN (character string) int isbn_num[13]; //array for ISBN (numeric) int main() { char y_n = 'y'; //sentinel int i, chk_valid, last_digit; // i=for counter, chk_vaild= switch, last dig= calculated last isbn digit hello(); //function call while(y_n =='y') { printf("\n\n Please enter you ISBN number"); scanf("%s",isbn); //reads isbn into character string isbm[] chk_valid = is_valid_isbn(isbn); //calls function to check for valid isbn if(chk_valid==1) { last_digit = check_digit_calc(); //recives calculated last digit if(isbn_num[9]==last_digit) printf(" \n\n The ISBN is valid\n\n"); else printf("\n\n You have entered an invalid ISBN \n\n"); } else printf("\n\n The ISBN you have entered contained non-numeric characters!\n\n"); printf("Do you wish to enter another ISBN number ?"); scanf("%c",&y_n); y_n=is_valid(y_n); //checks is user wants to continue system("cls"); } return 0; } void hello(void) //function to greet user { printf("\n *** Welcom to the ISBN check digit program where you enter and ISBN and we check it *****\n"); printf("\n ****How cool is that\a\..........**\n"); printf("\n **** Save your applause for after ****\n"); } char is_valid(char valid_y_n) { valid_y_n = tolower(valid_y_n); while(valid_y_n != 'y'&& valid_y_n != 'n') { printf("You can only enter 'y' or 'n'"); scanf("%c",&valid_y_n); valid_y_n = tolower(valid_y_n); } return (valid_y_n); int is_valid_isbn(char isbn[]) { int i, //counter loop j=0, //index for array invalid=1 ; char isbn_num1[1]; //singal digit string for atoi char *ptr_num1; // pointer for atoi ptr_num1 = &isbn_num1[0]; //initialization of pointer for atoi for (i = 0; i<strlen(isbn);i++) //loop to contiune to the end of the string { if(isbn[i] != '-') //gets rid of the hyphens and ignores them { if(isdigit(isbn[i]) == 0) //fail invalid = 0; //switch for main() else { isbn_num1[0] = isbn[i]; //stores characters as a string isbn_num[j] = atoi(ptr_num1); // stores characters in a form atoi() can use j++; } } } return(invalid); int check_digit_calc(void) //calculates check digit { int k, digit_total = 0, digit_value = 0; for( k = 0; k < 9; k++) digit_total += (k+1)* isbn_num[k]; digit_value = digit_total % 11; return (digit_value); }
