how to solve exit status 1 error? - c++

Question

I want to write c++ code which will separate all elements which have same length as input value
#include <iostream>
#include <vector>
using namespace std;
string database[] = {"green", "stupid", "boy", "girl", "forest", "mobile", "morning", "love", "keyboard", "incredible"};
string input;
string count(string input, string database[]){
string lengthFilter[] = {};
int inputLength = input.length();
for (int i = 0; i < database->length(); ++i){
if (database[i].length() == inputLength)
{
lengthFilter[lengthFilter->length()] = database[i];
}
}
return (lengthFilter);
}
int main()
{
cin >> input;
cout << count(input, database);
return 0;
}
but it gives error
main.cpp: In function 'std::__cxx11::string count(std::__cxx11::string, std::__cxx11::string*)':
main.cpp:16:22: error: could not convert 'lengthFilter' from 'std::__cxx11::string [0] {aka std::__cxx11::basic_string<char> [0]}' to 'std::__cxx11::string {aka std::__cxx11::basic_string<char>}'
return (lengthFilter);
^
exit status 1
I can't find my mistake, please, help me.

Answer 1

You stepped into the shortcomings of built-in C++ arrays and the [] syntax. This:
[]
Does not always mean what you think it means. Its meaning varies by context. In declarations:
string database[] = // ...
It means you're declaring a built-in array. However, in function arguments:
string count(string input, string database[])
it's a pointer. The above line is equivalent to:
string count(string input, string* database)
Also note that this:
string lengthFilter[] = {};
Declares a built-in array of zero size. I don't think this is what you want, since built-in arrays are fixed size. They don't resize.
So what you should be doing here, is use std::vector instead:
#include <iostream>
#include <vector>
using namespace std;
vector<string> database = {
"green", "stupid", "boy", "girl", "forest", "mobile", "morning", "love",
"keyboard", "incredible"
};
string input;
vector<string> count(string input, const vector<string>& database)
{
vector<string> lengthFilter;
auto inputLength = input.length();
for (const auto& i : database) {
if (i.length() == inputLength) {
lengthFilter.push_back(i);
}
}
return lengthFilter;
}
int main()
{
cin >> input;
for (const auto& i : count(input, database)) {
cout << i << '\n';
}
return 0;
}