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c       John Mahaffy,  Penn State University, CmpSc 201 Example
c       1/26/96
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c   Program to demonstrate Arithmetic Assignments
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program arith
implicit none
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c     declare the data types for all Fortran variables
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real r2,r3,r4,r5,r6,ans1,ans2,ans3
integer i2,i3,i4,i5,i6,ians1,ians2,ians3,ians4
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c     r2 thru r6 take on the real values 2.0 thru 6.0
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c     i2 thru i6 take on the integer values 2 thru 6
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c     ans1, ans2, and ans3 will contain the answers from
c     real arithmetic
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c     ians1 thru ians4 will contain the answers from
c     integer arithmetic
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c     Set initial values of the variables with 2 valid forms
c     of data statements
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data r2/2./,r3/3./,r4/4.0/,r5/5.0/
data i2,i3,i4,i5/2,3,4,5/
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c
c     This ends the non-executable statements, nothing above
c     this point results in a machine instruction to perform
c     some operation.
c     Executable statements follow.
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c     The result of any integer divide is truncated to the integer
c     value less than the correct decimal answer for the division
c     The result of this is that changing the order of operations
c     can make a big difference in the answers.  Notice how parentheses
c     force more expected results
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ians1=i2*i3/i5
ians2=i3/i5*i2
ians3=i2*(i3/i5)
ians4=(i3/i5)*i2
print *, '2*3/5 =', ians1, ', 3/5*2 =',ians2,
&  ', 2*(3/5) =',ians3 ,', (3/5)*2 =',ians4
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c     Real arithmetic behaves more uniformly
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ans1=r2*r3/r5
ans2=r3/r5*r2
ans3=(r3/r5)*r2
print *, '2.0*3.0/5.0 =', ans1, ', 3.0/5.0*2.0 =',ans2,
&  ', (3.0/5.0)*2.0 =',ans3
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c     Watch how precedence of operations effects the following:
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ians1=i2+i5*i3**i2
ians2=i5*i3**i2+i2
ians3=i3**i2*i5+i2
print *, '2+5*3**2 =',ians1,', 5*3**2+2 =',ians2,
& ', 3**2*5+2 =',ians3
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c     You can mix real and integers, but watch what happens
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ans1=r5+i3/i2
print *, '5.0+3/2 =',ans1

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c     You can do the same thing with constants in the expression
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ans2=5.0+3/2
print *, '5.0+3/2 =',ans2
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c     Look at what happens when I put a real in either the numerator
c     or denominator of the division term
ans1=r5+i3/r2
ans2=r5+r3/i2
print *, '5.0+3/2.0 =',ans1, ', 5.0+3.0/2 =', ans2
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c
c     Although Fortran normally works from left to right at a given
c     level of precedence (does all multiply and divide from left to
c     right before moving on to adds and subtracts).  It works
c     exponentiation from right to left when it hits 2 or more
c     sequential exponentiation operations
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ians1= i5**i3**i2
ians2= (i5**i3)**i2
ians3= i5**(i3**i2)
print *, '5**3**2 =',ians1, ', (5**3)**2 =',ians2,
&  ', 5**(3**2) =',ians3
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c    When in doubt use parentheses to get the answer that you
c    really want.
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stop
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end
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