smarty array index

I have an array

array('foo_1' => 1, 'bar_1' =>1, 'foo_2' => 2, 'bar_2' => 2, ... )

for($i = 1; $i<=12; $i++){
    echo $month['foo_'.$i];
}

And I don't understand how can I access the values from it using Smarty.

{counter start=0 skip=1 assign="i"}
 {section name = month start = 0 loop = 12 step = 1}
  {if isset($arr.开发者_如何学运维foo_.$i)}
   {$arr.bar_$i}
  {/if}
  {counter}
 {/section}

But it doesn't work. The main issue is - How I can access array['foo_1'] in smarty ? Can you please help?

You must build the key before accessing it in the array. Use assign to build the complete name.

{assign var=fooKey value="foo_"|cat:$i}
{assign var=barKey value="bar_"|cat:$i}
{if isset($arr.{$fooKey})}
  {$arr.{$barKey}}
{/if}

Your attempt {$arr.foo_.$i} means accessing the subkey $i in the array under $arr.foo_.