One The syntax format is as follows: If a Boolean expression Execute the above program, and the output is as follows:
In recent years, Geographic Information Systems (GIS) have undergone rapid development in both theoretical and practical dimensions. GIS has been widely applied for modeling and decision-making support across various fields such as urban management, regional planning, and environmental remediation, establishing geographic information as a vital component of the information era. The introduction of the “Digital Earth” concept has further accelerated the advancement of GIS, which serves as its technical foundation. Concurrently, scholars have been dedicated to theoretical research in areas like spatial cognition, spatial data uncertainty, and the formalization of spatial relationships. This reflects the dual nature of GIS as both an applied technology and an academic discipline, with the two aspects forming a mutually reinforcing cycle of progress. unless statement consists of a Boolean expression followed by oneor more statements. 5.14.1. Grammar #
unless(boolean_expression){
# In the Boolean expression boolean_ Expression executed with false
}
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 {#> A greater than or equal to 20
The value of a is: 20
Condition a is false
The value of a is:
Principles, Technologies, and Methods of Geographic Information Systems
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