Chapter 1 program process control box AutoLISP file (1) program Process Control

The process of The AUTOLISP program is controlled by flow control functions.

1. Branch Structure

(1) (cond (test expression 1 Result Expression 1) [(test expression 2 Result Expression 2)]...)

[Example]

1 (setq n( cond((<= i 1) 1)2              ((<= i 1) 1)3              ((<= i 2) 4)4              ((<= i 3) 10)5              (t 100)6         )7 )

Note: This function is similar to the switch statement in C language. The last test expression "t (or t)" is equivalent to "default" and refers to other cases. This test expression is also missing. Different from the C language switch, if a test expression is true, the value of the corresponding result expression is returned. If I is equal to 0, n is 1, and the operation ends.

(2) (if test condition expression 1 [expression 2])

If the expression of the test condition is true, expression 1 is executed. Otherwise, expression 2 is executed. for example: (if (> A 1) (setq B 2) meaning: if A is greater than 1, B is equal to 2. Otherwise, no calculation is performed and the evaluation ends. (If (> A 1) (setq B 2) (setq B 2) indicates that, if A is greater than 1, B is equal to 2; otherwise, B is equal to 3, and the end of the evaluate.

When a conditional expression is set, the progn function is required to execute multiple expressions.

(3) (progn expression ......)

(if(> a 1)    (progn (setq b 2)           (print (+ b a))           )    (progn (setq b 4)           (print b)           ))

Explanation: if the condition is true, B is equal to 2, and the sum of A and B is printed, and the sum of A and B is returned. Otherwise, B equals 4, print B, and return the value of B.

2. Loop Structure

(1) (Repeat integer N expression ......)

Repeat n times. Evaluate multiple expressions and return the calculation result of the last expression.

1 (setq a 1 b 100)2 (repeat 103　　 (setq a(+ 1 a))4 　　(setq b(+ 10 b))5 )

(2) (while test expression ......)

 (setq i 1 a 10) (while ( <=  i 10)　　 (setq a(+ a 10))　　(setq i(1+ i)) )

I don't know why there are always errors.

Solution: Because <= needs to be connected and written

Chapter 1 program process control box AutoLISP file (1) program Process Control