Question

如果我只使用我的功能一次，它可以正常工作。如果我让它做一个像下面的循环，四行注释代码，我的代码出现故障。我无法弄清楚为什么它会在初始值之后为每个其他数字返回T或F.

Asterisks在WRITE和READ的括号中，但由于某种原因它不会出现在这里。

PROGRAM PRIME

INTEGER :: N = 0, i = 1,x = 0

LOGICAL :: IP

WRITE (*,*) "Enter a number:"

READ (*,*) N

!DO WHILE ( N < 1000)

IP = IsPrime(N)

WRITE (*,*) IP, N

!N = N + 1

!END DO

read(*,*) x

CONTAINS

FUNCTION IsPrime(N)

LOGICAL :: IsPrime

INTEGER, INTENT(IN) :: N

IsPrime = .TRUE.

IF (N == 2) THEN

WRITE (*,*) N

ELSE 

DO WHILE (i <= (N/2))

   i = i + 2

   IF (mod(N,i) == 0) THEN 

   IsPrime = .FALSE.

   END IF

END DO

END IF


RETURN

END FUNCTION IsPrime

END PROGRAM PRIME

Answer 1

You're forgetting to reset i to 1 during each call to IsPrime.

The first time IsPrime is called, i=1 from the top of program main. However, i is incremented during the first IsPrime call to something other than 1 so the second call starts with i/=0.

Note that because IsPrime is contained within program main, IsPrime inherits i from program main.

I'm also bound to remind you to use implicit none everywhere to avoid other errors, although it's not a problem in this case.

FORTRAN逻辑没有问题

1 个答案: