Check if element found in array c++

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How can I check if my array has an element I'm looking for?

In Java, I would do something like this:

Foo someObject = new Foo(someParameter);
Foo foo;
//search through Foo[] arr
for(int i = 0; i < arr.length; i++){
  if arr[i].equals(someObject)
    foo = arr[i];
}
if (foo == null)
  System.out.println("Not found!");
else
  System.out.println("Found!");

But in C++ I don't think I'm allowed to search if an Object is null so what would be the C++ solution?

In C++ you would use std::find, and check if the resultant pointer points to the end of the range, like this:

Foo array[10];
... // Init the array here
Foo *foo = std::find(std::begin(array), std::end(array), someObject);
// When the element is not found, std::find returns the end of the range
if (foo != std::end(array)) {
    cerr << "Found at position " << std::distance(array, foo) << endl;
} else {
    cerr << "Not found" << endl;
}

Check if element found in array c++, In C++ you would use std::find , and check if the resultant pointer points to the end of the range, like this: Foo array[10]; // Init the array here Foo *foo� In this post, we will see how to check existence of given element in an array in C#. The solution should return true if array contains the specified value; otherwise, false. 1. Enumerable.Contains Method (System.Linq) The Enumerable.Contains method provides a simple, clean way to determines whether a sequence contains a specified element or …

There are many ways...one is to use the std::find() algorithm, e.g.

#include <algorithm>

int myArray[] = { 3, 2, 1, 0, 1, 2, 3 };
size_t myArraySize = sizeof(myArray) / sizeof(int);
int *end = myArray + myArraySize;
// find the value 0:
int *result = std::find(myArray, end, 0);
if (result != end) {
  // found value at "result" pointer location...
}

C Programming - Finding a Value in an Array, Program FIND_IDX.C ** ** Illustrates function to find the first occurance of a specified value ** in an array. If the specified value does not exist, function returns� C Program to Search an Element in an Array. This program asks the user to enter the Array size, Array elements, and the Search item value. Next, this C Program to Search an Element in an Array will check whether the user entered search item is present in the array or not using For Loop.

You would just do the same thing, looping through the array to search for the term you want. Of course if it's a sorted array this would be much faster, so something similar to prehaps:

for(int i = 0; i < arraySize; i++){
     if(array[i] == itemToFind){
         break;
     }
}

Check if an array contains all elements of a given range , Write a function to check if the array contains all elements in the given range. If an element is found such that |arr[i]| >= A and |arr[i]|. C++� Required knowledge. Basic Input Output, If else, For loop, Array. Logic to search element in array. There are two searching techniques linear and binary. For simplicity, I am implementing linear search algorithm to search element in array.

You can use old C-style programming to do the job. This will require little knowledge about C++. Good for beginners.

For modern C++ language you usually accomplish this through lambda, function objects, ... or algorithm: find, find_if, any_of, for_each, or the new for (auto& v : container) { } syntax. find class algorithm takes more lines of code. You may also write you own template find function for your particular need.

Here is my sample code

#include <iostream>
#include <functional>
#include <algorithm>
#include <vector>

using namespace std;

/**
 * This is old C-like style.  It is mostly gong from 
 * modern C++ programming.  You can still use this
 * since you need to know very little about C++.
 * @param storeSize you have to know the size of store
 *    How many elements are in the array.
 * @return the index of the element in the array,
 *   if not found return -1
 */
int in_array(const int store[], const int storeSize, const int query) {
   for (size_t i=0; i<storeSize; ++i) {
      if (store[i] == query) {
         return i;
      }
   }
   return -1;
}

void testfind() {
   int iarr[] = { 3, 6, 8, 33, 77, 63, 7, 11 };

   // for beginners, it is good to practice a looping method
   int query = 7;
   if (in_array(iarr, 8, query) != -1) {
      cout << query << " is in the array\n";
   }

   // using vector or list, ... any container in C++
   vector<int> vecint{ 3, 6, 8, 33, 77, 63, 7, 11 };
   auto it=find(vecint.begin(), vecint.end(), query);
   cout << "using find()\n";
   if (it != vecint.end()) {
      cout << "found " << query << " in the container\n";
   }
   else {
      cout << "your query: " << query << " is not inside the container\n";
   }

   using namespace std::placeholders;
   // here the query variable is bound to the `equal_to` function 
   // object (defined in std)
   cout << "using any_of\n";
   if (any_of(vecint.begin(), vecint.end(), bind(equal_to<int>(), _1, query))) {
      cout << "found " << query << " in the container\n";
   }
   else {
      cout << "your query: " << query << " is not inside the container\n";
   }

   // using lambda, here I am capturing the query variable
   // into the lambda function
   cout << "using any_of with lambda:\n";
   if (any_of(vecint.begin(), vecint.end(),
            [query](int val)->bool{ return val==query; })) {
      cout << "found " << query << " in the container\n";
   }
   else {
      cout << "your query: " << query << " is not inside the container\n";
   }
}

int main(int argc, char* argv[]) {
   testfind();

   return 0;
}

Say this file is named 'testalgorithm.cpp' you need to compile it with

g++ -std=c++11 -o testalgorithm testalgorithm.cpp

Hope this will help. Please update or add if I have made any mistake.

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If you were originally looking for the answer to this question (int value in sorted (Ascending) int array), then you can use the following code that performs a binary search (fastest result):

static inline bool exists(int ints[], int size, int k) // array, array's size, searched value
{
    if (size <= 0)      // check that array size is not null or negative
         return false;
    // sort(ints, ints + size); // uncomment this line if array wasn't previously sorted
    return (std::binary_search(ints, ints + size, k));
}

edit: Also works for unsorted int array if uncommenting sort.

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in_array - Manual, Loose checking returns some crazy, counter-intuitive results when used with certain arrays. Checks if an element is found in an array or one of its subarray. Parameters. needle. The searched value. Note: . If needle is a string, the comparison is done in a case-sensitive manner.. haystack. The array. strict. If the third parameter strict is set to TRUE then the in_array() function will also check the types of the needle in the haystack.

C Program to Search an Element in an Array, Next, this C Program to Search an Element in an Array will check whether the user entered search item is present in the array or not using For Loop. Check if an element exists in an array (fulfilling some criteria), and if so, proceed working with the first such element. If the intent is: To check whether an element exist in an array (/fulfils some boolean criteria, not necessarily equality testing), And if so, proceed and work with the first such element,

Check if an element is present in a set in C++, The standard solution to check for existence of an element in the set container ( std::set or std::unordered_set ) is to use its member function – find() . If the specified� Required knowledge. Basic Input Output, If else, For loop, Array. Logic to count frequency of each element of array. Finding frequency of each array element is based on logic to find duplicate elements in array.

Comments
  • Where is 10 coming from?
  • @JamesMcMahon That's the arbitrary number I picked for array size in my example.
  • As this is used as a duplicate target, and C++11 is now 5 years old, consider replacing array+10 with std::end(array)?
  • @Yakk Sure, that's the right thing to do! I also used std::distance while I'm at it. Thank you very much!
  • When I attempt it this way, it says that the "!operator" not found for my object.
  • Or you could try (foo == NULL)