5. Perl

  • 5.17. Perl switch statement

    One switch statement allows you to test when a variable is equal to multiple values. Each value is called a case, and th...
    2025-10-25 13:33:03 UTC
  • 5.18. Perl cycle

    Sometimes, we may need to execute the same piece of code multiple times. In general, statements are executed sequentially: t...
    2025-10-25 13:33:01 UTC
  • 5.19. Perl while cycle

    while statement when a given condition is true the statement or group of statements is executed repeatedly. The cond...
    2025-10-25 13:33:04 UTC
  • 5.21. Perl for cycle

    Perl for loops are used to execute a sequence of statements multiple times, simplifying the code that manages loop varia...
    2025-10-25 13:33:01 UTC
  • 5.22. Perl foreach cycle

    Perl foreach loop is used to iterate over the value of a list or collection variable. 5.22.1. Grammar # The syn...
    2025-10-25 13:33:06 UTC
  • 5.23. Perl do…while cycle

    Not like for and while loops, they test the loop conditions at theloop header. In Perl the language do...while...
    2025-10-25 13:33:02 UTC
  • 5.24. Perl loop nesting

    Perl language allows the use of another loop within one loop, and here are a few examples to illustrate this concept. ...
    2025-10-25 13:33:00 UTC
  • 5.25. Perl next statement

    Perl next statement is used to stop execution from the next the statement between the beginning of the next statemen...
    2025-10-25 13:33:05 UTC
  • 5.26. Perl last statement

    Perl last statement is used to exit the loop statement block, thus ending the loop last the statement after the stat...
    2025-10-25 13:33:00 UTC
  • 5.27. Perl continue statement

    Perl continue blocks are usually executed before the conditional statement is judged again. continue statement can...
    2025-10-25 13:33:01 UTC
  • 5.28. Perl redo statement

    Perl redo statement directly to the first line of the body of the loop to repeat the execution of the loop redo stat...
    2025-10-25 13:33:02 UTC
  • 5.29. Perl goto statement

    Perl has three forms of goto : got LABLE , goto EXPR , and goto &NAME : Serial number ...
    2025-10-25 13:33:06 UTC
  • 5.30. Perl operator

    An operator is a symbol that tells the compiler to perform specific mathematical or logical operations, such as: 3+2=5 ....
    2025-10-25 13:33:04 UTC
  • 5.31. Perl time date

    In this chapter, we introduce to you Perl treatment of time and date by language. There are several functions for proc...
    2025-10-25 13:33:06 UTC
  • 5.32. Perl subroutine (function)

    Perl subroutines are user-defined functions. Perl subroutine is a separate piece of code that performs a particula...
    2025-10-25 13:33:00 UTC
  • 5.33. Perl reference

    A reference is a pointer. Perl reference is a scalar type that can point to variables, arrays, hash tables (also known a...
    2025-10-25 13:33:02 UTC
《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。