Sequence
Selection
Loop
Subprogram

Computer instructions reflect the operations a computer can perform and the tasks we want it to accomplish:

• Transfer data from one location to another
• Input data from a device and output data to a device
• Store data in memory and retrieve data from memory
• Compare data values for equality or inequality
• Perform arithmetic operations

Control structures are used to express algorithms as programs. Four basic ways to structure statements (instructions) in most languages are:

• Sequentially
  Statements executed one after another in order
• Conditionally
  IF ... THEN
• Repetitively
  Loops: WHILE ( condition )... LOOP; DO ... LOOP; FOR ( condition )... NEXT
• Via Subprograms
  Procedure, Function, Method, Subroutine
  CALL ( subprog ) ... RETURN

Sequential Program Control

Conditional Program Control

Repetitive Program Control

Control via Subprograms
Also called procedure, function, method, or subroutine