IF condition comparing a substring to a string array produces error in C++

Question

I am just a beginner in C++ and I am trying to scan the first character of an inputted string for vowels using simple syntaxes

I tried using array of strings for vowels

string vowels[] = {"a","e","i","o","u"};
string word;
string first;

cout<< "enter a word: ";
cin>>word;
cout<<endl;

first = word.substr(0,1);

cout<<first<<endl;

if (first == vowels)
{
    cout << "NO!"<<endl;
}
else
{
    cout<< word <<endl;
}


return 0;

if condition yields an error:

Invalid operands to binary expression ('string' (aka 'basic_string, allocator >') and 'string *' (aka 'basic_string, allocator > *'))

Possible duplicate of C++ comparing a string with an array of strings — walnut
– walnut, Commented Sep 30, 2019 at 2:23

Foxhound · Accepted Answer · 2019-09-30 04:34:09Z

0

You're trying to too see if a word(first) is identical to an array (vowels).

What you need to be doing is check if each character inside the word is also contained inside the vowel array.

A simple function do this would look something like.

bool insideArray( std::string aWord, std::string aArray[] )
{
    for(unsigned int i = 0; i< aWord.length(); i++ ) 
    {
        //Use the find function.
        bool exists = std::find( std:begin(aArray, std:end(aArray), aWord[i]) != std:end(aWord[i])
        if (exists) {
            return true;
        } 
    }
    // reached the end, and have never returned true, so no character from aWord is inside aArray
    return true
}

edited Sep 30, 2019 at 4:34

answered Sep 30, 2019 at 4:27

Foxhound

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Comments

LegendofPedro · Accepted Answer · 2019-09-30 02:29:35Z

-1

You need to compare first to each element of vowels[].

for(int i=0; i<vowels.size(); i++) {
    if(first == vowels[i])
        // ...
}

answered Sep 30, 2019 at 2:29

LegendofPedro

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4 Comments

Sydney Born Over a year ago

I am getting an error: Member reference base type 'string [5]' is not a structure or union

walnut Over a year ago

vowels is an array, so vowels.size() won't work. That said, @SydneyBorn should prefer std::vector<std::string> over a raw array.

LegendofPedro Over a year ago

array::size() is added in C++11. Perhaps you could use (sizeof(vowels)/sizeof(*vowels)) to determine the array length instead.

walnut Over a year ago

@LegendofPedro OP is using a raw array, so std::array::size won't help either. A better way to get the length of a raw array (and any std container) is std::size (since C++17)

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