Control Flow - Control Structures in Practice

Control Structures in Practice

Most programming languages with control structures have an initial keyword which indicates the type of control structure involved. Languages then divide as to whether or not control structures have a final keyword.

• No final keyword: Algol 60, C, C++, Haskell, Java, Pascal, Perl, PHP, PL/I, Python, PowerShell. Such languages need some way of grouping statements together:
  • Algol 60 and Pascal : begin ... end
  • C, C++, Java, Perl, PHP, and PowerShell: curly brackets { ... }
  • PL/1: DO ... END
  • Python: uses indentation level (see Off-side rule)
  • Haskell: either indentation level or curly brackets can be used, and they can be freely mixed
• Final keyword: Ada, Algol 68, Modula-2, Fortran 77, Mythryl, Visual Basic. The forms of the final keyword vary:
  • Ada: final keyword is end + space + initial keyword e.g. if ... end if, loop ... end loop
  • Algol 68, Mythryl: initial keyword spelled backwards e.g. if ... fi, case ... esac
  • Fortran 77: final keyword is end + initial keyword e.g. IF ... ENDIF, DO ... ENDDO
  • Modula-2: same final keyword END for everything
  • Visual Basic: every control structure has its own keyword. If ... End If; For ... Next; Do ... Loop; While ... Wend