Program to check for ISBN | PHP program to check if a given ISBN is valid or not . ; length must be 10 ; Computing weighted sum of first 9 digits ; Checking last digit . ; If last digit is ' X ' , add 10 to sum , else add its value . ; Return true if weighted sum of digits is divisible by 11. ; Driver code
< ? php function isValidISBN ( $ isbn ) { $ n = strlen ( $ isbn ) ; if ( $ n != 10 ) return -1 ; $ sum = 0 ; for ( $ i = 0 ; $ i < 9 ; $ i ++ ) { $ digit = $ isbn [ $ i ] - '0' ; if ( 0 > $ digit 9 < $ digit ) return -1 ; $ sum += ( $ digit * ( 10 - $ i ) ) ; } $ last = $ isbn [ 9 ] ; if ( $ last != ' X ' && ( $ last < '0' $ last > '9' ) ) return -1 ; $ sum += ( ( $ last == ' X ' ) ? 10 : ( $ last - '0' ) ) ; return ( $ sum % 11 == 0 ) ; } $ isbn = "007462542X " ; if ( isValidISBN ( $ isbn ) ) echo " Valid " ; else echo " Invalid " ; ? >