Why aren't 2 chars equal?

This is a discussion on Why aren't 2 chars equal? within the C++ Programming forums, part of the General Programming Boards category; I'm new with c++ programming and i got this newb guestion. I got 2 variables, char a[5] = "hola"; and ...

  1. #1
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    Why aren't 2 chars equal?

    I'm new with c++ programming and i got this newb guestion.
    I got 2 variables, char a[5] = "hola"; and char b[5] = "hola";.
    The problem is that when i check them like this:
    Code:
    char a[5] = "hola";
    char b[5] = "hola";
    
    if(a == b) {
    cout << "Hello to you too\n";
    }
    else {
    cout << "No hello to you\n";
    }
    it says "No hello to you".
    So what i want to ask is why aren't those equal and how can i make variables a and b equal?

  2. #2
    Lean Mean Coding Machine KONI's Avatar
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    You are not comparing two "chars" but actually you are comparing pointer to char arrays, which are two completely different things. Since you are not using the std::string type (that supports comparison using the == operation), you have to understand how C strings work.

    In fact, a and b are pointers to the first element of each respective array. Imagine that they do not contain a specific character but rather an address to the location where the first character of the array is located. If the address of a is "0000" and the address of b is "1000", then when you write a==b, you effectively compare the two addresses, which, as you can see, are different.

    If you want to compare two C strings, use the strcmp() function that does the job for you:

    Code:
    char a[5] = "hola";
    char b[5] = "hola";
    
    if (strcmp(a,b) == 0)
    {
    cout << "Hello to you too\n";
    }
    else
    {
    cout << "No hello to you\n";
    }
    Since you are programming in C++, you could just write:
    Code:
    std::string a, b;
    a = "hola";
    b = "hola";
    if(a == b) {
    cout << "Hello to you too\n";
    }
    else {
    cout << "No hello to you\n";
    }
    since then you're using the overloaded comparison operator of the string object.

  3. #3
    and the hat of wrongness Salem's Avatar
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    It's a good job you didn't try

    char *a = "hola";
    char *b = "hola";
    if(a == b)

    Which might be the right answer for entirely the wrong reason
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  4. #4
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    Thanks, that made alot sense.

  5. #5
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    If you are new to C++ you should not be using character arrays to store strings. Use the C++ string class instead.

  6. #6
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by Salem View Post
    It's a good job you didn't try

    char *a = "hola";
    char *b = "hola";
    if(a == b)

    Which might be the right answer for entirely the wrong reason
    Sometimes I use a string caching layer which inserts strings into a hash table and returns a pointer to the instance of the string in the hash. If you do this consistently, you CAN compare strings for equality by just checking if the pointers are equal

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