Why echo() affects the output of this code so much?

Question

I don't get the logic behind this piece of code 🤔.

The original code outputs 17. Why?
Trying to figure out what is going on using echos changes the final output to more predictable 1. Why? Also {} were omitted in the if-else section. Why?!!

Please explain it to me 🙏

Answer 1

Sorry 😐 I couldn't insert the code in the question. I tried.

https://code.sololearn.com/wRG35NTF5CZO/?ref=app

Answer 2

𝙛𝙞𝙧𝙨𝙩 𝙥𝙖𝙧𝙩 :

I don't know about php but in some languages i have seen only first statement being executed without curly braces.

I did a small google search and as i told you above is what is happening here.

https://stackoverflow.com/questions/8726339/php-if-else-for-foreach-while-without-curly-braces/8726411#:~:text=12%20Answers&text=When%20you%20omit%20the%20braces,as%20body%20of%20the%20condition.&text=Internally%20it's%20the%20other%20way,a%20single%20%22grouped%22%20expression.&text=There%20are%20places%20where%20you%20can%2C%20but%20you%20never%20should.

Print "taran=".$taran." a=".$a."<br>" After the global statement to get an idea of what is happening .

But i will still try to explain you .

The following function calls are taking place,
num(5)
num(4)
num(3)
num(2)
num(1)
num(0)
num(1-3) // when code encounters value 0 , recursion for else statement stop and the call is returned back to num($a-3) with value of 1 .

num(2-3)
num(3-3)

Answer 3

𝙨𝙚𝙘𝙤𝙣𝙙 𝙥𝙖𝙧𝙩:

num(4-3) //again recursion(inner recursion) starts because 1 is greater than 0.

num(1-1)
num(1-3)
num(5-3)
num(2-1)
num(1-1)
num(1-3)
num(2-3)

Basically there are two types of recursion happening , one is inner and second is outer which makes it quite hard to understand what is going on, but if you really want to understand, take a copy and pen and start drawing the steps that are taking place .