Pangram checker

You are encouraged to solve this task according to the task description, using any language you may know.
A pangram is a sentence that contains all the letters of the English alphabet at least once.

For example:   The quick brown fox jumps over the lazy dog.



Task

Write a function or method to check a sentence to see if it is a   pangram   (or not)   and show its use.



Related tasks

   determine if a string has all the same characters
   determine if a string has all unique characters


DECLARE FUNCTION IsPangram! (sentence AS STRING)
 
DIM x AS STRING
 
x = "My dog has fleas."
GOSUB doIt
x = "The lazy dog jumps over the quick brown fox."
GOSUB doIt
x = "Jackdaws love my big sphinx of quartz."
GOSUB doIt
x = "What's a jackdaw?"
GOSUB doIt
 
END
 
doIt:
    PRINT IsPangram!(x), x
    RETURN
 
FUNCTION IsPangram! (sentence AS STRING)
    'returns -1 (true) if sentence is a pangram, 0 (false) otherwise
    DIM l AS INTEGER, s AS STRING, t AS INTEGER
    DIM letters(25) AS INTEGER
 
    FOR l = 1 TO LEN(sentence)
        s = UCASE$(MID$(sentence, l, 1))
        SELECT CASE s
            CASE "A" TO "Z"
                t = ASC(s) - 65
                letters(t) = 1
        END SELECT
    NEXT
 
    FOR l = 0 TO 25
        IF letters(l) < 1 THEN
            IsPangram! = 0
            EXIT FUNCTION
        END IF
    NEXT
 
    IsPangram! = -1
END FUNCTION