How to display the country capital even if the input is case insensitive c+

Question

I've working on this code for quite a while and I can't find how to make this case insensitive

#include <iostream>
#include <string>
#include <sstream>
using namespace std;

int findCountry(string arr[], int len, string seek)
{
    for (int i = 0; i < len; ++i)
    {
        if (arr[i] == seek) return i;
    }
    return -1;
}

int main(){
    string countries[5]={"Brunei", "Cambodia", "East Timor", "Indonesia", "Laos"};
    string capitals[5]={"Bandar Seri Begawan", "Phnom Penh", "Dili", "Jakarta", "Vientiane"};
        
    string country;
    
    cout << "Country: ";
    cin >> country;
    
    int index = findCountry(countries,5,country);
     if (index >= 0)
        cout << "Capital: " << capitals[index];
    else
        cout << country << " is not a South East Asian Country";
    
    return 0;
}

OUTPUT

Country: bRunEi
bRunEi is not a South East Asian Country

Expected OUTPUT

Country: bRunEi
Capital: Bandar Seri Begawan

I was instructed to use cstring header but this is the only thing I can guess, any help will be appreciated ps: sorry for bad english

Side note: the overall approach using two arrays `countries` and `capitals` is wrong. You should use a `struct` or a `class`. — Jabberwocky, May 02 '22 at 13:33
@Jabberwocky It is absolutely _not_ wrong — many industrial applications use parallel arrays like this to good effect. I agree that OP should use a `struct`, though. — Dúthomhas, May 02 '22 at 13:42
Heh, two good answers below. Make sure to get input using `getline(cin, country)` too. — Dúthomhas, May 02 '22 at 13:46
@Dúthomhas Having parallel is maybe not _wrong_ but it's dangerous, because you need to keep them in sync. For 5 entries it may be manageable, but for 100 entries it's painful, let alone having more than 2 parallel arrays. — Jabberwocky, May 02 '22 at 13:48
An app that relies on parallel arrays better have indexing arrays included with them, for things like sorting and lookup, and as @Jabberwocky mentioned, keeping things in sync. Can you imagine having to sort 100 separate arrays if you want to sort by a certain criteria? — PaulMcKenzie, May 02 '22 at 14:29

Captain Giraffe · Answer 1 · 2022-05-02T15:22:22.447

There are a few points of improvements that can simplify your code.

Firstly if you use a standard container for your countries.

std::vector<std::string> countries = {"Brunei", "Cambodia", "East Timor", "Indonesia", "Laos"};

For having case insensitive input you transform using https://en.cppreference.com/w/cpp/string/byte/tolower or its sibling toupper.

std::tolower is in the <cctype> header, but I'd supppose that is a part of <cstring>.

The reference contains a usage example that covers you case.

std::string str_tolower(std::string s) {
    std::transform(s.begin(), s.end(), s.begin(), 
                [](unsigned char c){ return std::tolower(c); }
                  );
    return s;
}

std::transform is in the header, you should have a look in there for many simple algorithms, that allows you to describe your code in a simpler way than using a regular for-loop like you are doing in findCountry. Look at the algoritm std::find, for instance.

The expression [](unsigned char c){ ... } is a lambda expression, extremely useful combined with the algorithms. https://en.cppreference.com/w/cpp/language/lambda

Thank you very much, ill try this one as well – First Gate May 02 '22 at 14:20 — First Gate, May 02 '22 at 14:20

wohlstad · Answer 2 · 2022-05-02T17:34:12.480

Regarding the case insensitive comparison:

You can use the function IsEqualStringsCaseInsensitive below to compare 2 strings ignoring the case. You can call it instead of using (arr[i] == seek) to compare strings.

#include <string>
#include <cctype>

bool IsEqualStringsCaseInsensitive(std::string const & s1, std::string const & s2)
{
    size_t len1 = s1.length();
    size_t len2 = s2.length();
    if (len1 != len2) {
        return false;
    }
    for (size_t i = 0; i < len1; ++i) {
        if (isascii(s1[i]) && isascii(s2[i])) {
            // Both are ASCII - compare lower case version:
            if (std::tolower(s1[i]) != std::tolower(s2[i])) {
                return false;
            }
        }
        else {
            // Compare as-is:
            if (s1[i] != s2[i]) {
                return false;
            }
        }
    }
    return true;
}

A few additional notes about your code:

In general it's better to use std::vector<std::string> const & arr instead of old style C arrays (string arr[]).
Better to avoid using namespace std - see here Why is "using namespace std;" considered bad practice?.
You can pass seek by const& to avoid copy.

UPDATE: Based on the comment below by @EvilTeach (that std::tolower is valid only for ASCII characters), I modified my code above. It now calls std::tolower only if both characters are ASCII. Otherwise compares as-is (there's no meaning for case sensitivity at least for one of them, which means they must be identical, for string equality).

I suggest verifying that the values are ASCII before using tolower on them as tolower is only valid for ASCII — EvilTeach, May 02 '22 at 16:20
@EvilTeach can you give an example of a non ASCII character in a `std::string` (that causes a problem with `std::tolower`) ? — wohlstad, May 02 '22 at 16:23
https://stackoverflow.com/questions/37799582/how-to-use-tolower-function-for-non-ascii-characters — EvilTeach, May 02 '22 at 16:37

How to display the country capital even if the input is case insensitive c+

2 Answers2