33 lines
1.2 KiB
Text
33 lines
1.2 KiB
Text
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; 1. Check the least significant bit.
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(define (even? i)
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(if (eq? (band i 1) 0) #t #f))
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(define (odd? i)
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(if (eq? (band i 1) 1) #t #f))
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(print (if (even? 12345678987654321) "even" "odd")) ; ==> odd
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(print (if (odd? 12345678987654321) "odd" "even")) ; ==> odd
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(print (if (even? 1234567898765432) "even" "odd")) ; ==> even
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(print (if (odd? 1234567898765432) "odd" "even")) ; ==> even
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; 2. Divide i by 2. The remainder equals 0 iff i is even.
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(define (even? i)
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(if (eq? (remainder i 2) 0) #t #f))
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(define (odd? i)
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(if (eq? (remainder i 2) 1) #t #f))
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(print (if (even? 12345678987654321) "even" "odd")) ; ==> odd
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(print (if (odd? 12345678987654321) "odd" "even")) ; ==> odd
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(print (if (even? 1234567898765432) "even" "odd")) ; ==> even
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(print (if (odd? 1234567898765432) "odd" "even")) ; ==> even
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; 3. Use modular congruences. Same as 2.
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(define (even? i)
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(if (eq? (mod i 2) 0) #t #f))
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(define (odd? i)
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(if (eq? (mod i 2) 1) #t #f))
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(print (if (even? 12345678987654321) "even" "odd")) ; ==> odd
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(print (if (odd? 12345678987654321) "odd" "even")) ; ==> odd
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(print (if (even? 1234567898765432) "even" "odd")) ; ==> even
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(print (if (odd? 1234567898765432) "odd" "even")) ; ==> even
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