How smarty implements I ++

How does smarty implement I ++ on html pages? How does smarty implement I ++?
How can I translate the following C # code into the code under smarty?

<%                   int i_count = 0;                    foreach (GridViewRow row in this.GridView1.Rows)                   {                          if (i_count%4 == 0)                          {%>                                 
.1..
<%                          }                          else                           {%>                                 
.2..
<%                            }                           i_count ++ ;                    }%>

I wrote this, but ERROR

                   {assign var="i_count"}                   {foreach from=$row item=item}                                             {if $i_count mod 4}                                                           
.2..
                                                  {else}                                                            
.1..
                           {/if}                           {$i_count + 1 }                    {/foreach}

How can I write it? Is it my I ++ error?

Reply to discussion (solution)

Why do you want to write it like this? In smarty foreach, you can obtain the {foreach from = $ var key = k item = v} of the current key}
This k is enough.

{assign var="i_count" value=0}                   {foreach from=$row item=item}                                              {if $i_count mod 4}                                                            
.2..
                                                   {else}                                                             
.1..
                           {/if} {assign var="i_count" value=$i_count+1}                    {/foreach}

No test. if not, use ''for $ I _count + 1.

Plain Text code? 1234567891011121314 {assign var = "I _count" value = 0} {foreach from = $ row item = item} {if $ I _count mod 4 }......

It seems to be caused by '', but why does my code execute the content in the first p for the first time and then all the content in the second p?

                    {if $i_count mod 4 == 0}                  
.1..
                   {else}                   
.2..
                   {/if} 

{foreach from=$row item=item key=i_count}                                            {if $i_count mod 4}                                                             
.2..
                                                    {else}                                                              
.1..
                           {/if}

{foreach from=$row item=item key=i_count}{if ($i_count mod 4)==0}
.2..
{else}
.1..
{/if}

This sentence can be written in this way.

{if ($i_count mod 4) eq 0}