3.4 Strings

1. Exam Points

• String manipulation:
  • String concatenation: concat(str1, str2)
  • Get a substring: substring(str, start, length) (看题目里的函数怎么给的).
  • Get the length of a string: len(str)
  • Reverse a string: Ex. abc -> cba
• More operations: refer to procedures given in questions.

2. Knowledge Points

(1) Strings (字符串)

• A string is an ordered sequence of characters.
• Example:
  • Annabelle
  • 13697665261
  • ID Number (身份证号)
• Each character in a string can be located by its index, which starts from 1.

(2) String Manipulation (字符串操作)

• String concatenation(字符串连接) : joins together two or more strings end-to-end to make a new string.
  • Example:

    •     concat("abc","def")  
          
          Result: abcdef
          ```
      

    •     x ← 18 
          concat("age: ",x)
          
          Result: age: 18
          ```
      

• A substring is part of an existing string.
  • Example:

    •     Case 1: Substring(str, start, length)
          name ← "Annabelle" 
          Substring(name, 5, 4) 
          
          Result: bell
          
          Case 2: Substring(str, start, end)
          name ← "Annabelle" 
          Substring(name, 5, 8) 
          
          Result: bell
          ```        
      

• Revsere a string.
  • Example:

    •     str1 ← "abcd" 
          str2 ← reverse(str1)
          str3 ← concat(str1,reverse(str1))
          
          Value of str2: dcba
          Value of str3: abcddcba
          ```   
      

• Get the length (number of characters) of a string.
  • Example:

    •     str ← "abcd" 
          length ← len(str)
          
          Value of length: 4
          ```   
      

3. Exercises

• Practice
• Solution