Prolog101(04)

数学计算:
X is <数学表达式> 

数学运算:
+-*/
()

比较运算:
X > Y 
X < Y 
X >= Y 
X =< Y  
1 ?- X is 1*2+3/4-(5-6)*7.
X = 9.75.

2 ?- 3=<4.
true.

3 ?- 3>=4.
false.

4 ?- 3>4.
false.

5 ?- 3<4.
true.

6 ?- X is 2+2, 3>=X.  
false.

看一下摄氏度与华氏度互转的程序:

%swipl -s calc.pl
%Hansen

c_to_f(C,F) :- F is C*9/5+32.
f_to_c(F,C) :- C is (F-32)*5/9.
1 ?- c_to_f(11,F).
F = 51.8.

2 ?- f_to_c(51.8,F).
F = 10.999999999999998.

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