Error in calling function passing string as a parameter in c++

Question

This is my code, upon compiling it is showing error in type conversion when I am calling isVowel( ) function.Can you check and tell what's the error?

#include <iostream>
#include <string>
#include <typeinfo>
using namespace std;
bool isVowel(string a)
{
    if(a == "a" || a =="e" || a =="i" || a =="o" ||a =="u"){
        return true;
    }
    else
        return false;
}

int main()
{
    int T;
    cin>>T;
    for (int i = 0; i < T; i++)
    {
        string s, snew="";
        cin>>s;
        for (int j=0;j<s.length();j++)
        {
            if(isVowel(s[j]))
                continue;
            else
                snew += s[j];
        }
    }
    return 0;
}

*Always* include the error message you get, in your question - *verbatim*. — Jesper Juhl, Apr 17 '18 at 17:31
String can hold a single character, but a single character is not a string. — user4581301, Apr 17 '18 at 17:32
@SauravBhagat It can, but that doesn't make them the same type. — Barmar, Apr 17 '18 at 17:32
yes, but you need `isVowel(s.substring(j,1)` to extract a one char string. — pm100, Apr 17 '18 at 17:32
@JesperJuhl I am sorry will take care of this from next time. If I am changing the string to char in function definition, then I am getting this error. ISO C++ forbids comparison between pointer and integer [-fpermissive] — Saurav Bhagat, Apr 17 '18 at 17:33
A `char` is an integer type. `"a"` is not a character or a string. It is a string literal. In this case it is a `const char[2]`. This is [decayed to a pointer](https://stackoverflow.com/questions/1461432/what-is-array-decaying) for the comparison, resulting in the integer to pointer error. — user4581301, Apr 17 '18 at 17:36

dbush · Answer 1 · 2018-04-17T17:37:22.687

5

You function is expecting a string but you're passing in a char. While a string can hold a single character, it's not the same thing. The types need to match.

Change the function to expect a char, and use character constants instead of string constants for the comparisons so comparing a char with a char. Also, because you're simply returning true or false if the condition is true or false, just return the result of the comparison expression.

bool isVowel(char a)
{
    return (a == 'a' || a =='e' || a =='i' || a =='o' || a =='u');
}

edited Apr 17 '18 at 17:37

answered Apr 17 '18 at 17:31

dbush

205,898
23
218
273

Construction `if( ... ) return true; else return false;` looks ugly. Is there something wrong with me? – Slava Apr 17 '18 at 17:35
Shouldn't it be `if(a == 'a' || a =='e' || a =='i' || a =='o' ||a =='u' || sometimes(a == 'y'))` ;) – NathanOliver Apr 17 '18 at 17:35
@NathanOliver OP may have different definition of vowel – Slava Apr 17 '18 at 17:37
Dang it @NathanOliver ! 'y' must you make things so hard? – user4581301 Apr 17 '18 at 17:37
@Slava Yeah, that is ugly. Fixed. – dbush Apr 17 '18 at 17:38
One could search a string of vowels, instead of the comparison. – Thomas Matthews Apr 17 '18 at 18:11

score 3 · Answer 2 · answered Apr 17 '18 at 17:50

3

Use library functions when possible:

bool isVowel( char a )
{
    return std::string( "aeiouy" ).find( a ) != std::string::npos;
}

std::copy_if( source.begin(), source.end(), std::back_inserter( target ),
    []( char c ) { return not isVowel( c ); } );

live example

answered Apr 17 '18 at 17:50

Slava

43,454
1
47
90

In C++17 you can even use a `std::string_view` instead to avoid any possible dynamic allocation. – NathanOliver Apr 17 '18 at 17:55

score 1 · Answer 3 · answered Apr 17 '18 at 18:15

For starters vowels can have upper or lower case.

Your function declaration is wrong

bool isVowel(string a);

The function should check the supplied character whether it is a vowel.

The function can be defined the following way as it is shown in the demonstrative program.

#include <iostream>
#include <string>
#include <iterator>
#include <algorithm>
#include <functional>
#include <cstring>
#include <cctype>

bool isVowel( char c )
{
    const char *vowels = "aeiou";

    return c != '\0' && std::strchr( vowels, std::tolower( ( unsigned char )c ) );
}

int main() 
{
    std::string s( "Hello Saurav Bhagat" );
    std::string new_s;

    std::copy_if( s.begin(), s.end(), std::back_inserter( new_s ),
        std::not1( std::function<bool( char )>( isVowel ) ) );

    std::cout << s << std::endl;        
    std::cout << new_s << std::endl;        

    return 0;
}

Its output is

Hello Saurav Bhagat
Hll Srv Bhgt

Error in calling function passing string as a parameter in c++

3 Answers3