CODEWITHSUNDEEP
loopswhile-loopfortran
Eray Xx
Eray Xx

Reputation: 313

Why does my program end in an endless loop?

I can't understand why it's happening but it becomes an endless loop when I start the program. What do I do wrong ?

 program Hello
  REAL K1,K2,RP,G,m,t,time,R1,R2
  G = 6.67384 * (10**(-11))   
  m = 5.9723E24       
  t = 0.1               
  RP = 6371000               
  K1 = 15                    
  K2 = 10                         
  R1 = K1 + RP
  R2 = K2 + RP
  r = R1
  DO WHILE (r > R2)
    r = r - ((Gm*t/r**2)*t)
    time = time + t
  END DO
 write (*,*) "Time = seconds" 
 write (*,*) (Gm*t/r**2) 
 end program Hello

Upvotes: 2

Views: 76

Answers (1)

Vladimir F Героям слава
Vladimir F Героям слава

Reputation: 59999

Gm is not declared and is implicitly to be real. The value of Gm is not set, but it is very likely 0. Therefore r is the same all the time.

You probably wanted to type G*m but you have Gm in ((Gm*t/r**2)*t).

Always use implicit none in your programs. It is VERY important.

And as you found yourself 10**(-11) is zero, because it is an integer expression. E or D must be used for exponent in floating point expressions.

Upvotes: 3

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