Finding maximum characters for each filed in a table

DECLARE
@c varchar(4000),
@t varchar(128),
@maxchars int,
@fieldName varchar(100),
@dynamicSql nvarchar(2000)
SET @c = ''
SET @t='LEGACY_GMM'
SET @maxchars = 0
SET @fieldName = ''
SET @dynamicSql = ''
SELECT @c = @c + c.name + ', '
FROM syscolumns c
INNER JOIN sysobjects o ON o.id = c.id
WHERE o.name = 'LEGACY_GMM' and c.colorder < 101
while charindex(',', @c) > 0
begin
SET @fieldName = substring(@c,0,charindex(',',@c))
SET @dynamicSql = 'select max(len(' + @fieldName + ')) as ' + @fieldName + ' from LEGACY_GMM;'
execute sp_executesql @dynamicSql
SET @c = substring(@c, charindex(',',@c)+1, LEN(@c))
end