5.14. Perl UNLESS statement

One unless statement consists of a Boolean expression followed by oneor more statements.

5.14.1. Grammar #

The syntax format is as follows:

unless(boolean_expression){ # In the Boolean expression boolean_ Expression executed with false } 

If a Boolean expression boolean_expression for false , then if block of code within the statement will be executed. If the Boolean expression is true , then if the first set of code at the end of the statement (after closing parentheses) is executed.

5.14.2. Flow chart #

Example #

#/ Usr/bin/perl $a=20# Using the 'less' statement to detect the Boolean expression' less' ($a<20 "; "a # $a 'a' 'condition ($a) ){# 20 : ; < a boolean detect equal execute expression false false, greater is: less n n"; n";} n';} of or pre print printf statement than the to use value when {#>

Execute the above program, and the output is as follows:

 A greater than or equal to 20 The value of a is: 20 Condition a is false The value of a is:  

文章链接： 5.14. Perl UNLESS statement

Web框架 946

《地理信息系统原理、技术与方法》 97

最近几年来，地理信息系统无论是在理论上还是应用上都处在一个飞速发展的阶段。 GIS被应用于多个领域的建模和决策支持，如城市管理、区划、环境整治等等，地理信息成为信息时代重要的组成部分之一； “数字地球”概念的提出，更进一步推动了作为其技术支撑的GIS的发展。与此同时，一些学者致力于相关的理论研究，如空间感知、空间数据误差、空间关系的形式化等等。这恰好说明了地理信息系统作为应用技术和学科的两个方面，并且这两个方面构成了相互促进的发展过程。

WEB基础 289