Adding strings in CCK Computed field

Hi Guys,

I have recently joined NZ Drupal Group. I am a Junior Developer and am bit stuck on something. I am hoping somebody can help me out here.

I have a field called:
field_a | Type: text
field_b | Type:computed

so in my computed field I would like to do:

if ($node->field_a[0]['value']){
$var1="some text";
$var2="some more text";

$node_field[0]['value']="$var1.$node->field_a[0]['value'].$var2";

This doesn't display anything. I tried creating temporary arrays as well to achive the same thing but that doesn't work either. I am just wondering if this is the correct way to go about doing this or is there any other better method.

Please do advise and thank you for your time. Cheers.