C# - How to use operator for numbers in an array

Question

I have an int array that store age values. I want to print all the values in the array which are above or eqaul to 18.

int[] age = new int[] { 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30 };
      
foreach(int item in age)
{

}

I tried something like this but didn't work.

int[] age = new int[] { 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30 };
int targetAge = 18;
int findedAge = Array.FindIndex(age, age => age == targetAge);

if (age>= targetAge)
{
    foreach (int item in age)
    {
        Console.WriteLine(item);
    }
}

FindIndex returns the index of the first element that's equal to targetAge(18). Also, even if you retrieve this value that's wrong you are not using it, so it is useless. You are also comparing an array (age) to an integer. This operation can't be done because the two objects cannot be compared, it's like comparing apple and pears — Matteo Umili
– Matteo Umili, Commented Jul 20, 2022 at 8:23

Dmyto Holota · Accepted Answer · 2022-07-20 08:25:01Z

3

To filter the array you can do this:

var resultArray = age.Where(item => item >= 18).ToArray();

or use the FindAll:

var resultArray = Array.FindAll(age, item => item >= 18);

The first option uses an extension methods named Where that operates on IEnumerable, which arrays implement. IEnumerable is an interface for a sequence of elements that can be stepped through one after the other.

The second option uses FindAll, which is actually built in to the Array class.

For more info you can look at this post.

answered Jul 20, 2022 at 8:25

Dmyto Holota

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4 Comments

tmaj Over a year ago

You'll need using System.Linq; for this to work.

Matteo Umili Over a year ago

Your solution is surely correct, but I like more the one provided by @tymtam because it provides better performance and less memory usage (I find no difference in terms of readability)

Charlieface Over a year ago

@MatteoUmili Removing .ToArray would reduce memory usage

teamol Over a year ago

Yeah, .ToArray() is abundant here if the only thing OP needs to do is foreach and WriteLine.

tmaj · Accepted Answer · 2022-07-20 08:20:10Z

2

You are so close!

foreach (int item in age)
{
    if (item>= targetAge)
    {
        Console.WriteLine(item);
    }
}

answered Jul 20, 2022 at 8:20

tmaj

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2 Comments

tmaj Over a year ago

There are two changes here: 1. You have if outside of foreach and that's incorrect. 2. It's if (item >= , not if (age>=

Matteo Umili Over a year ago

@IndieDev if the code you wrote is the real one then age is an int[], so item must be an int. You also wrote that targetAge is an int so the code wrote by @tymtam is correct

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