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in this code i'm comparing between two strings i did it correctly, but i don't want to consider the letters' case.

for ex: first string: aaaa, second string: aaaA. the output should be 0 or equal.

is there any ideas to fix this?

#include <iostream>
#include <algorithm>
#include <string>
using namespace std;
int main() 
{
    cout << "enter the first string" << endl;
    string x; 
    cin >> x;
    cout << "enter the second string" << endl;
    string y; 
    cin >> y;
    cout << endl;
    sort(x.begin(), x.end());
    sort(y.begin(), y.end());
    cout << x << endl;
    cout << y << endl;
    if (x.compare(y) < 0)
    {
        cout << "-1" << endl;
    }
    if (x.compare(y) > 0)
    {
        cout << "1" << endl;
    }
    if (x.compare(y) == 0)
    {
        cout << "0" << endl;
    }

}
Konrad Rudolph
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Osama Nagi
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  • You could transform both input strings to lowercase prior to comparison; see e.g. [How to convert std::string to lower case?](https://stackoverflow.com/questions/313970/how-to-convert-stdstring-to-lower-case). – dfrib Jun 16 '20 at 07:30
  • @dfri No, that is a **bad solution**. It will fail for some international strings. – Konrad Rudolph Jun 16 '20 at 07:31
  • @KonradRudolph Ah I was not aware this was the case for `std::basic_string`, thanks. – dfrib Jun 16 '20 at 07:33
  • lowercase 2 strings before comparing them. – Hieu Doan Jun 16 '20 at 07:33
  • @dfri My concern is unrelated with `std::basic_string`, it applies to *every* string type in *every* programming language. Admittedly C++ strings are even worse since `tolower` and `toupper` are broken. – Konrad Rudolph Jun 16 '20 at 07:35

2 Answers2

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You can use std::tolower to convert the strings x and y to its lower case representation and than compare the two lowercase strings.

#include <algorithm>

...
if (std::tolower(x) == std::tolower(y)) { 
    ...
}
...
schorsch312
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  • Don’t use `tolower` or `toupper` to implement case insensitive compare. This will fail for `x = "STRASSE"` and `y = "straße"`, which should compare equal. – Konrad Rudolph Jun 16 '20 at 07:36
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    Why should "STRASSE" and "straße" are equal? "SS" is not equal to "ß". – schorsch312 Jun 16 '20 at 07:57
  • Because that’s what the rules of German orthography say (DIN 5007-1). – Konrad Rudolph Jun 16 '20 at 08:02
  • That is wrong. The word "Strasse" does not exist in the German language. "Straße" is correct. https://www.korrekturen.de/beliebte_fehler/strasse.shtml Currently, an uppercase "ß" has been introduced. https://de.wikipedia.org/wiki/Gro%C3%9Fes_%C3%9F – schorsch312 Jun 16 '20 at 08:08
  • That’s all pretty irrelevant. String comparison (generally) doesn’t limit itself to “existing” words (for a given definition of “existing”), it controls string collation. Otherwise you could also say that “straße” isn’t a word in German, only “Straße” is. Yet if you walk through your town you should notice that the spelling “STRASSE” *does* exist in actual fact, even in highly official artefacts. – Konrad Rudolph Jun 16 '20 at 08:18
  • The OP asked for a case insensitive string comparison. What you are mentioning is a semantic comparison. – schorsch312 Jun 16 '20 at 08:22
  • No. I am *not* talking about “semantic” comparison, I’m talking purely about (case insensitive) string comparison, semantics play no role. This is all well-defined in Unicode, but C++ does not implement it natively. You need to use a library that handles strings correctly. Strings in C++ are merely byte sequences, not correct character sequences (despite the misleading data type name). – Konrad Rudolph Jun 16 '20 at 08:25
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Solution from here

if (std::toupper(x) == std::toupper(y)) {
    cout << "0" << endl;
}
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