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For Loop in different programming languages

Rattanak Chea on October 06, 2017

Programming often involves working on redundant tasks. The for loops help shorten the code and reduce tedious tasks. But the way for is used can be...

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Ben Halpern • Oct 6 '17

Love the apples-to-apples comparison.

Here's Ruby:

for num in 0..max_num do
   puts "The number is #{num}"
end

But in practice, nobody uses for loops.

Here's a while:

while num < max_num  do
   puts("The number is #{num}" )
   num +=1
end

But nobody uses those either.

People are way more likely to do

(0..max_num).each do |num|
   puts "The number is is #{num}"
end

Or using a collection of objects, like an array or an ActiveRecord collection.

pizza_toppings.each do |topping|
   puts "The topping is #{topping.name}"
end

Rattanak Chea • Oct 6 '17

Thank you for adding Ruby syntax. This post was written a few year ago when I found myself always scrambling to write loop when working with different programming languages. Nowadays, a functional programming approach is preferable. I love Python and Ruby for their clean syntax.

Rattanak Chea • Oct 6 '17

Do you mind if I include your Ruby code into the post? I will put credit where it belongs.

Ben Halpern • Oct 6 '17

Go for it. And no need to credit if it effects the reading in any way. 🙂

Harry • Oct 7 '17

There's a few other ways to iterate in JavaScript:

for-of

const array = [1,2,3];
for (const num of array) {
  console.log(num);
}

forEach

const array = [1,2,3];
array.forEach(num => {
  console.log(num);
};
// or
array.forEach(console.log);

Functional programming - map

const array = [1,2,3];
array.map(console.log);

Harry • Oct 7 '17 • Edited

Note: forEach(console.log) will print the item, index and the array - developer.mozilla.org/en-US/docs/W...

Array#forEach((item, index, array) => { /*...*/ })

Unknown • Oct 12 '17

There is no need to use breckets in lambda:

const array = [1,2,3];
array.forEach(num => console.log(num));

Antonin J. (they/them) • Oct 6 '17

Here's one for Go:

myStr := "My string"

for i := 0; i < len(myStr); i++ {
  fmt.Printf("%c", myStr[i])
}

You can also use a while loop:

for _, char := range myStr {
  fmt.Printf("%c", char)
}

Note how a "while loop" is basically the same as a for loop.

Jeremy Mill • Oct 6 '17

Or in rust

let my_str = "Hello World!";    
for c in my_str.chars() { 
    print!("{}",c);
}

David Multer • Oct 6 '17

In Python, this:

for num in range(max_num):
    print "The number is {}".format(num)

or this:

print '\n'.join(["The number is {}".format(num) for num in range(max_num)])

Louis-Saglio • Nov 2 '17

It's why i use Python.

Dan Ross • Oct 6 '17 • Edited

Your PHP string foreach example seems wrong - PHP strings can be referenced like an array. The following works on PHP, for example.

$str = "hello";
for($i = 0; $i < strlen($str); $i++){
    echo $str[$i];
}

Rattanak Chea • Oct 7 '17

I did include that too, but it was down. Now i moved it to the top. Thanks man.

Everton Agner • Oct 10 '17 • Edited

Let's be fair with Java. The language has seen quite a few enhancements since Java 8 release, 3 years ago, and very recently on Java 9, both on API and syntax. Now using the new stuff...

Loop a string:

String str = "hello";
str.chars() // Produces a stream of integers... yeah, that's odd
    .mapToObj(i -> (char) i) // Now we have a stream of chars
    .forEach(System.out::println);

Loop a collection:

List<String> list = List.of("a", "b");
list.forEach(System.out::println);

Steven Salka • Oct 7 '17

Nice post! When working with JavaScript/TypeScript, I usually go for the forEach array method, which is pretty convenient for usage with functions:

const fruit = ['apple', 'banana', 'orange'];

fruit.forEach(console.log);
// apple
// banana
// orange

If using a library like lodash, you can also iterate over objects (though iteration order is not guaranteed):

const funcs = {
  square: x => x ** 2,
  abs: x => Math.abs(x),
  reciprocal: x => 1 / x
};

_.forEach(funcs, (fn, fnName) => {
  console.log(`${fnName}(-2) = ${fn(-2)}`);
});
// square(-2) = 4
// abs(-2) = 2
// reciprocal(-2) = -0.5

Miff • Oct 7 '17 • Edited

Here's the ways to loop a string and an array in C# with a for loop, they're pretty much the same as any other language.

    string str = "hello";
    for (int i = 0; i < str.Length; i++){
        Console.WriteLine(str[i]);
    }

    int[] nums = new int[5];
    for (int i = 0; i < nums.length; i++){
        nums[i] = i;
        Console.WriteLine(i);
    }

However, C# really likes iterators, so those tasks are most commonly done with a foreach loop.

    string str = "hello";
    foreach (char c in str){
        Console.WriteLine(c);
    }

    foreach (int num in Enumerable.Range(0, 5)){
        Console.WriteLine(num);
    }

    // Borrowing from Ben Halpern's example for looping over a collection
    foreach (var topping in pizzaToppings){
        Console.WriteLine("The topping is {0}", topping.Name);
    }

Chris Shepherd • Oct 7 '17

Then resharper tells you that you can replace that with one line of linq... if my experience is anything to go by 😀

Dmytro Pylypenko • Oct 7 '17 • Edited

Swift 2, 3, 4:

// 1
for index in 0..<9 {
    print(index)
}

// 2
(0..<9).forEach { index in
    print(index)
}

// 3
let arr = ["foo", "bar"]
for (index, value) in arr.enumerated() {
    print("index: \(index), value: \(value)")
}

Rattanak Chea • Oct 7 '17

I never learn/write Swift. Look interesting. Thanks for sharing.

Jason C. McDonald • Dec 8 '17

Very nice, but it's missing my favorite, C++!

std::string str = "hello";
for (int i=0; i < str.length(); ++i)
{
    std::cout << str[i] << std::endl;
}

Note I'm using the prefix increment in my for loop, for pedantic (and habitual) performance reasons. (In reality, your compiler usually optimizes this itself.)

Given more time later, I'll come back and add the other two.

KhoPhi • Oct 7 '17

I built a website ago just to keep how different programming languages approach concepts in their different ways.

Like the Fibonacci in 6 languages: code.khophi.co/codes/-KL7i0Vj9WSsh...

code.khophi.co

Rattanak Chea • Oct 7 '17

I checked it out. That's a good idea. Keep it up.

Thomas Graf • Dec 31 '17 • Edited

Java 9 IntStream has a new static method:

iterate(int seed, IntPredicate hasNext, IntUnaryOperator next)

IntStream.iterate(0, i -> i < 10, i -> i + 1)
            .forEach(System.out::println)

is equivalent to the following for-i loop, but more in a functional style

for(int i = 0; i < 10; i++) {
    System.out.println(i);
}

Inés Sosa • Oct 6 '17 • Edited

Here's in Smalltalk:

'Hello' do: [:each | Transcript show: each ]

this works for collections, strings, and objects all the same :D

Rattanak Chea • Oct 7 '17 • Edited

Awesome. One size fits all. :-)

Inés Sosa • Oct 8 '17

The wonders of dynamically typed languages 😊

Sayo Paul • Oct 6 '17

PHP code doesn't have syntax highlighting though 😀

Rattanak Chea • Oct 7 '17

I guess it is not support here yet. That's not fair for PHP. :-)

Ben Halpern • Oct 7 '17

I'm not quite sure why that is. Definitely looking into it.