// returns true or false depending on whether the ISBN// number passed to the function is valid or not.// // if it is not valid, the variable checksum will be the// correct checkdigit.bool isvalidISBN(char *dig,int *checksum){ remdash(dig); // removes the dashes from an ISBN number if (!atoi(dig)) return false; int checkdig = dig[strlen(dig)-1]-'0'; dig[strlen(dig)-1] = '\0'; int i,j = 2,total = 0; for (i = (int)strlen(dig)-1;i>=0;i--) { total += (dig[i] - '0') * j; j++; } int check = 11 - (total % 11); *checksum = check; if (checkdig == check) return true; else return false;}