User Input Validation Using Character Array in C++

Question

I am creating a c++ program to validate book ID using function in c++. The program must return 1 if the input is valid and 0 if the input is invalid. INPUT Pattern: "123-AB-12345" This will be considered as a valid input. The valid input is: (a) Total characters must be 12 (b) First three characters must be integers from 1 to 9 each. (c) 4th and 7th characters must be hiphen "-". (d) Last 5 characters must be integers from 1 to 9 each.

I tried the following way but I am not getting the desired answer. Need help plz

#include<iostream>
using namespace std;
bool isValidBookId(char bookId[13]);
int main()
{
    char book[13];
    cin.getline(book,12);
    bool id = isValidBookId(book);
    cout<<id;
}
bool isValidBookId(char bookId[13])
{
    int i;
    bool check1,check2,check3,check4,check5,check6;
    check1=check2=check3=check4=check5=true;
    if(bookId[12]=='\0'){
        check1=true;
    }       
    if(bookId[3]=='-')
    {
        check2=true;
    }
    if(bookId[6]=='-')
    {
        check3=true;
    }
    for(i=0; i<3;i++){
        if(bookId[i]>=0 || bookId[i]<=9)
        {
            check4=true;
        }
    }
    if(bookId[i]>= 'A' || bookId[i]<= 'Z')
    {
        check5=true;
    }
    for(i=7; i<12; i++)
    {
        if(bookId[i]>=0 || bookId[i]<=9)
        {
            check6=true;
        }
    }
    if(check1==true && check2==true && check3==true && check4==true && check5==true && check6==true)
    {
        return true;
    }
    else
    {
        return false;
    }
}

Answer 1

There's a few errors that you have in your code.

First, you initialize all your checks to true , and never set anything to false , so the answer will always be true . Realistically, you want to initialize them all to false , and change to true when all the conditions are met, or assume true , and set to false when the condition is not met.

Second, your check for the values 0-9 is incorrect. You cannot compare bookId[i] to 0 , you want to compare it to the character '0' . Also note that the question you have also says 1-9 not 0-9

Third, your check for AZ is incorrect (note, this issue also applies to 0-9 ). You're code basically says is bookId[i] greater than or equal to 'A' OR less than or equal to Z , which is always going to be true .

I've written your code below:

bool isValidBookId( char bookId[13] ) {

    if ( bookId[12] != '\0' )
        return false;
    if ( bookId[3] != '-' )
        return false;
    if ( bookId[6] != '-' )
        return false;

    for ( int i = 0; i < 3; i++ ) {
        if ( bookId[i] < '1' || bookId[i] > '9' ) {
            return false;
        }
    }
    for ( int i = 4; i < 6; i++ ) {
        if ( bookId[i] < 'A' || bookId[i] > 'Z' ) {
            return false;
        }
    }
    for ( int i = 7; i < 12; i++ ) {
        if ( bookId[i] < '1' || bookId[i] > '9' ) {
            return false;
        }
    }

    return true;
}

This method doesn't require any Boolean variables. Instead, I assume true (the last return statement) and instead try to prove false . As soon as something is false , you can return without doing any other checks.

Answer 2

Since the given code is in C-Style format, I would like to present 2 additional solutions in C++. I think the task is anyway to think about patterns and how these could be detected.

In my first solutions I just added more C++ elements. The 2nd solution should be the correct on.

Please see:

#include <iostream>
#include <regex>
#include <string>
#include <cctype>
#include <vector>

bool isValidBookId1(const std::string& bookId) {

    // Lambda to detect hyphen
    auto ishyphen = [](int i){ return static_cast<int>(i == '-');};

    // First check size of given string
    bool result{(bookId.size() == 12)};

    // Define the position of the types
    std::vector<size_t> digitIndex{0,1,2,7,8,9,10,11};
    std::vector<size_t> letterIndex{4,5};
    std::vector<size_t> hyphenIndex{3,6};

    // Check types
    if (result) for (size_t index : digitIndex) result = result && std::isdigit(bookId[index]);
    if (result) for (size_t index : letterIndex) result = result && std::isupper(bookId[index]);
    if (result) for (size_t index : hyphenIndex) result = result && ishyphen(bookId[index]);

    // Return resulting value
    return result;
}

bool isValidBookId2(const std::string& bookId) {

    // Define pattern as a regex
    std::regex re{R"(\d{3}-[A-Z]{2}-\d{5})"}; 

    // Check, if the book id matches the pattern
    return std::regex_match(bookId, re);
}

int main()
{
    // Get input from user
    if (std::string line{}; std::getline(std::cin, line)) {
        std::cout << "Check for valid Book input 1: " << isValidBookId1(line) << "\n";
        std::cout << "Check for valid Book input 2: " << isValidBookId2(line) << "\n";
    }
    return 0;
}