1.2.3 - Introduction to Programming

• Procedural Programming

  • widely-used paradigm
  • can be used for a wide range of problems
  • fairly easy to write/interpret
  • uses sequence of instructions usually contained in procdeures
  • these are carried out step by step
• Program Flow - Structures

  • sequence
  • selection
  • iteration
• Sequence

  • code executed line-by-line, top to bottom
• Selection

  • block of code is run if a certain condition is met
  • IF, ELSE IF and ELSE statements
• Iteration

  • block of code is executed a select number of times or while a condition is met
  • FOR, WHILE or REPEAT UNTIL loops
• Variables

  • named locations in memory where data is stored
  • contents of location can be changed while program is being executed
  • must be declared before use
  • sometimes need to be assigned a data type
• Constants

  • named locations in memory
  • value cannot be changed by program during execution
  • used for values that don't need to be changed (Pi, VAT)
  • prevents value from being changed accidentally
  • often capitalised (PI, VAT)
• Procedures

  • named blocks of code that perform a specific task
  • do not have to return a value
  • can return multiple values
  • usually given data as parameters
• Functions

  • named blocks of code that perform a specific task
  • must always return a value
  • can only return a single value
  • often use local variables
• Arithmetic Operators

  • used to carry out math functions in programs
• Arithmetic Operators - Examples

  • +, -, *, /
  • **
  • DIV or //
  • MOD or %
• **

  • exponentiation - raising a number to a power
  • 2**4 = 16
  • 2^4 = 16
• DIV or //

  • calculates whole number of times a number goes into another
  • integer division
  • 50 DIV 7 = 7
• MOD or %

  • used to find the remainder when a number is divided by another
  • 50 MOD 7 = 1
• Relational Operators

  • make comparisons between two values
  • produce result of True or False
• Relational Operators

  • > greater than
  • < less than
  • >= greater than or equal to
  • <= less than or equal to
  • != not equal to
  • == equal to
• Assembly Language

  • uses mnemonics instead of binary
  • each mnemonic is represented by a numeric code
  • commands used are processor-specific as they interact directly with CPU's special purpose registers
  • allows for direct interaction with hardware - useful in embedded systems
• Assembly Language - Mnemonics

  • ADD
  • SUB
  • STA
  • LDA
  • INP
  • OUT
  • HLT
  • DAT
  • BRZ
  • BRP
  • BRA
• ADD

  • add
  • adds value at given memory address to value in accumulator
• SUB

  • subtract
  • subtracts value at given memory address from value in accumulator
• STA

  • store
  • stores value in accumulator at given memory address
• LDA

  • load
  • load value at given memory address into accumulator
• INP

  • input
  • allows user to input a value that gets held in the accumulator
• OUT

  • output
  • prints value currently held in the accumulator
• HLT

  • halt
  • stops program at that line, stopping the rest of the code from executing
• DAT

  • data
  • creates a flag with a label at which data is stored
• BRZ

  • branch if zero
  • branches to given address if value in accumulator is zero
  • conditional branch
• BRP

  • branch if positive
  • branches to given address if value in accumulator is positive
  • conditional branch
• BRA

  • branch always
  • branches to given address no matter the value in the accumulator
  • unconditional branch