JuniorTheoryCommon

What does the program print?

PHP

<?php

function countdown(int $n): string
{
    if ($n === 0) {
        return 'go';
    }
    return $n . countdown($n - 1);
}

echo countdown(3), "\n";

321go

Expecting 123go, as if the deepest call came first: each call puts its own $n before the inner result, so the 3 of the outer call opens the string.
Expecting the base case to print first: return 'go' hands its value back to the caller, and every call above it adds its own $n in front.

What would countdown(-1) do, and how would you guard against it?
How would you change line 8 so that the program prints go123?

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JuniorTheoryCommon

What does the program print?

PHP

<?php

function countdown(int $n): string
{
    if ($n === 0) {
        return 'go';
    }
    return $n . countdown($n - 1);
}

echo countdown(3), "\n";

321go

Expecting 123go, as if the deepest call came first: each call puts its own $n before the inner result, so the 3 of the outer call opens the string.
Expecting the base case to print first: return 'go' hands its value back to the caller, and every call above it adds its own $n in front.

What would countdown(-1) do, and how would you guard against it?
How would you change line 8 so that the program prints go123?

Back to questions Open topic in roadmap →Answer it yourself — Quiz