[nepstep]

Strings without length means that you are not defining the strings length at the sscanf for example this will bring a warning:
if(sscanf(params, "us", giveplayerid, reason))
when this won't bring one:
if(sscanf(params, "us[64]", giveplayerid, reason))
and about the "No default value" warning it means that when you are asking for an optional value and its not given it will return an error.
Example of a sscanf that will bring warning:
if(sscanf(params, "uS[64]", giveplayerid, optionalvalue)) where optionalvalue is not required
and example of a good one without warning:
if(sscanf(params, "uS[64](default optional value)", giveplayerid, optionalvalue)) this will set optional value to "default optional value" if its not given
where "64" is the strings size