How can I check if given int exists in array?

Question

For example, I have this array:

int myArray[] = { 3, 6, 8, 33 };

How to check if given variable x is in it?

Do I have to write my own function and loop the array, or is there in modern c++ equivalent to in_array in PHP?

Look at the example for [`std::find`](http://www.cplusplus.com/reference/algorithm/find/). — DCoder, Oct 10 '13 at 15:08

juanchopanza · Accepted Answer · 2017-10-18T19:52:39.483

58

You can use std::find for this:

#include <algorithm> // for std::find
#include <iterator> // for std::begin, std::end

int main () 
{
  int a[] = {3, 6, 8, 33};
  int x = 8;
  bool exists = std::find(std::begin(a), std::end(a), x) != std::end(a);
}

std::find returns an iterator to the first occurrence of x, or an iterator to one-past the end of the range if x is not found.

edited Oct 18 '17 at 19:52

answered Oct 10 '13 at 15:10

juanchopanza

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3

Or simply: `bool exists = std::any_of(std::begin(array), std::end(array), [&](int i) { return i == x; });` – Zac Howland Oct 10 '13 at 15:15
2

`std::find` is nice if you aren't on C++ 11. Then again `std:begin` and `std:end` are C++ 11 only. – James McMahon Apr 17 '15 at 16:58
How can I do it on a non-hardcoded array? Error no matching function for call to 'std::begin'` Like this `int *squaresPlayerMarked = new int[5](); int x = 8; bool exists = std::find(std::begin(squaresPlayerMarked), std::end(a), squaresPlayerMarked) != std::end(a); std::cout << exists;` – Mote Zart Feb 04 '21 at 04:48
@MoteZart All you have is a pointer, so you need to keep track of the array length, and then use it to get the past-the-end iterator, for example `squaresPlayerMarked + 5`. – juanchopanza Feb 04 '21 at 20:24

Zac Howland · Answer 2 · 2013-10-10T15:19:26.977

I think you are looking for std::any_of, which will return a true/false answer to detect if an element is in a container (array, vector, deque, etc.)

int val = SOME_VALUE; // this is the value you are searching for
bool exists = std::any_of(std::begin(myArray), std::end(myArray), [&](int i)
{
    return i == val;
});

If you want to know where the element is, std::find will return an iterator to the first element matching whatever criteria you provide (or a predicate you give it).

int val = SOME_VALUE;
int* pVal = std::find(std::begin(myArray), std::end(myArray), val);
if (pVal == std::end(myArray))
{
    // not found
}
else
{
    // found
}

John Dibling · Answer 3 · 2013-10-10T15:31:00.080

You almost never have to write your own loops in C++. Here, you can use std::find.

const int toFind = 42;
int* found = std::find (myArray, std::end (myArray), toFind);
if (found != std::end (myArray))
{
  std::cout << "Found.\n"
}
else
{
  std::cout << "Not found.\n";
}

std::end requires C++11. Without it, you can find the number of elements in the array with:

const size_t numElements = sizeof (myArray) / sizeof (myArray[0]);

...and the end with:

int* end = myArray + numElements;

score 2 · Answer 4 · answered Oct 10 '13 at 15:15

Try this

#include <iostream>
#include <algorithm>


int main () {
  int myArray[] = { 3 ,6 ,8, 33 };
  int x = 8;

  if (std::any_of(std::begin(myArray), std::end(myArray), [=](int n){return n == x;}))   {
      std::cout << "found match/" << std::endl;
  }

  return 0;

}

score 1 · Answer 5 · answered Oct 10 '13 at 15:14

1

int index = std::distance(std::begin(myArray), std::find(begin(myArray), end(std::myArray), VALUE));

Returns an invalid index (length of the array) if not found.

answered Oct 10 '13 at 15:14

Neil Kirk

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score -4 · Answer 6 · edited May 23 '17 at 12:32

-4

You do need to loop through it. C++ does not implement any simpler way to do this when you are dealing with primitive type arrays.

also see this answer: C++ check if element exists in array

edited May 23 '17 at 12:32

Community

1
1

answered Oct 10 '13 at 15:11

zirror

1

1

Yes it does -- std::find. It's still a loop in the end, but a loop that's already been written. – John Dibling Oct 10 '13 at 15:13
The linked question even has an answer involving std::find_first_of... – badgerr Oct 10 '13 at 15:14
`std::find`, `std::find_first_of`, `std::any_of`. They all implement loops, but the language has provided them for you (so you do not need to write your own). In C++, most of the time you will rarely have to write your own loop. – Zac Howland Oct 10 '13 at 15:25
The language provides overloads of `std::(c)(r)(begin|end)` for raw arrays so that they can be processed by algorithms using unified syntax. Even before those debuted, pointers into (or, of course, one-past-the-end of) raw arrays could be used as iterators. Like, iterators are a _superset_ of pointers, so of course. – underscore_d Jul 18 '17 at 18:38

How can I check if given int exists in array?

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