For loops in zsh and bash

Question

I have noticed there are two alternative ways of building loops in zsh:

1. for x (1 2 3); do echo $x; done
2. for x in 1 2 3; do echo $x; done

They both print:

1
2
3

My question is, why the two syntaxes? Is $x iterating through a different type of object in each of them?

Does bash make a similar distinction?

Addendum:

Why does the following work?:

#!/bin/zsh
a=1
b=2
c=5    

d=(a b c)    
for x in $d; do print $x;done

but this one doesn't?:

#!/bin/zsh
a=1
b=2
c=5

d=(a b c)    
# It complains with "parse error near `$d'"
for x $d; do print $x;done 

Answer 1

Several forms of complex commands such as loops have alternate forms in zsh. These forms are mostly inspired by the C shell, which was fairly common when zsh was young but has now disappeared. These alternate forms act exactly like the normal forms, they're just a different syntax. They're slightly shorter, but less clear.

The standard form for the for command is for x in 1 2 3; do echo $x; done, and the standard form for the while command is while test …; do somecommand; done. Ksh, bash and zsh have an alternate form of for: for ((i = 0; i < 42; i++)); do somecommand; done, which mimics the for loops of languages like Pascal or C, to enumerate integers. Other exotic forms that exist in zsh are specific to zsh (but often inspired by csh).