Introduction to Computer Programming

Introduction to Computer Programming

• A computer program features a set of instructions that performs specific tasks when executed by the computer's central processing unit.
• Sequence is the order in which program instructions are carried out, defining the order or pattern of execution.
• Pattern types include linear (straight line) and incremental (following number patterns), directing the OS to move after each instruction.
• Instructions are commands sent to the CPU to manage computing tasks, including actions like copy, print, delete, and mathematical operations.
• BODMAS, meaning Brackets, Orders, Division, Multiplication, Addition, Subtraction, is a math rule.
• A series of task-attempting steps with statements are written by a programmer in human-readable source code.
• Steps 1, 2, and 3 contribute to a set of instructions where each step builds on the previous one, forming a method for a particular purpose.
• A computer program is a set of instructions designed to complete a task.
• Programmers enter steps as methods in text editors designed for specific programming languages.
• A programming environment consists of a text editor and tools like library functions.
• Examples of programming environments include Macromedia Dreamweaver, Visual Studio, and Bloodshed Dev C++.
• Library functions are pre-defined operations within a programming environment, like Addition, subtraction, and Division.
• ADD and PRINT are library functions that command the computer to add and print results, respectively.
• Source code comprises functions within a programming environment in a human-readable format.
• The CPU compiles the source code to create an executable program (machine code), suitable for distribution as computer software.

Definition of Source Code

• Source code is human-readable text that specifies actions for a computer, which is then converted to binary machine code.
• Computer programming involves creating a sequence of executable instructions to automate a computational task.
• Software is a collection of computer programs, libraries, and associated data, while software development includes design, implementation, and maintenance.

Program Operation

• At the computer's operational level, a program is a series of numeric codes, directly converted by the hardware into basic operations for complex tasks.
• The numerical codes of a program exist in binary form and are stored in the computer's memory
• The instruction set is the collection of numerical codes that directs the computer to perform simple operations.
• A typical digital computer instruction set includes data transfer, arithmetic operations, shift operations, and transfer of control.
• Data transfer moves data within the processor, between the computer and its memory, or between the processor and external devices.
• Arithmetic operations instruct the computer to perform calculations and logical operations like AND, OR, NOT, and XOR.
• Shift operations move data left or right within a register or memory location.
• Transfer of control directs the machine to skip instructions or repeat previous ones.
• A combination of instruction types is executed by retrieving each instruction from memory, decoding the required operation, and performing it under the processor's direction, known as the fetch-execute cycle.
• The next instruction is automatically fetched from storage after each instruction, ending when a halt instruction is recognized.

Machine Code

• A computer loads numbers into registers, adds them, and stores the result in memory using a machine code program.
• Each instruction, starting at memory location 1000, is fetched, decoded, and executed.
• The process continues until instruction 1007, the halt instruction, is decoded.
• Binary code in the instruction allows the CPU to control the hardware and perform the necessary operations.
• A machine code instruction set consists of binary codes that the control unit can decode to carry out operations.
• Programming languages allow programmers to focus on problem-solving instead of machine code conversion.

Low-Level Languages

• Assembly languages were a significant innovation as they are more readable than machine code
• Mnemonic devices replace function codes for easier recall.
• LDA is used for LOAD ACCUMULATOR as an example of a mnemonic
• Addresses and operands use programmer-defined labels or names
• Assembly language instructions generally translate to one machine code instruction

Assembly Language

• Load Register RO with the contents of location N1(LDR R0,N1)

• Load Register R1 with the contents of location N2 (LDR R1,N2)

• Add RO and r1 and store in RO (ADD R0,R1 )

• Store register R0 in location N3 (STR R0,N3)

• Halt execution of program (HLT)

• The operation codes, LOAD, ADD, STORE, and HALT, correspond to LDR, ADD, SDR, and HLT.

• The assembler converts assembly language into machine code since processors cannot decode assembly directly.

• The assembler takes assembly language as data, converts it into numerical equivalents, assigns memory addresses, and outputs machine code.

• There is one to one correspondence between a machine code instruction and one in assembly language, where assembly language is the source, and machine code is the object

• Machine code requires no translator is one advantage it has over assemblers

• Computers can also use machine code in a fast and efficient way

Machine Language & Assembly Code

• Machine language requires memorization of all operation codes and memory addresses
• Assembly code is better because mnemonics and symbolic labels are easier to remember and to understand.
• Symbolic addresses in assembly programs can be changed without altering the operand's address.
• An assembler translates assembly language programs into machine code

Disadvantages of Assembly Language

• Assembly code takes a lot of time to type
• Assembly code can be vulnerable to bugs
• Machine dependent, therefore, users can't get any output due to its architecture.
• An assembler translates source programs into machine code; determines storage location; links programs; and prints source/object program listings.

High-Level Programming

• High-level languages focus on problem-solving rather than the computer's specifics.
• High-level instructions translate into multiple machine code instructions.
• Generalized instructions in high-level languages, such as arithmetic expressions, require complex translators.
• High-level languages simplify programs to single statements (N3 = N1 + N2), representing memory address storage.
• Programmers don't have to worry about the precise mechanics since the translator does this automatically

History of High-Level Languages

• Like computer hardware, high-level languages are categorized by generation.
• First-generation languages are based on computer architecture and instruction sets.
• Data structures are based on internal representations, and punched cards are used for input, FORTRAN is an example.
• Second-generation languages refined first-generation structures; overall structure design was better, using structured programming as a result.
• Programs were using more flexible statements (e.g., ALGOL 60).
• Third-generation languages adopted user-defined data structures, simplified control structures, and became more hardware-independent (e.g., PASCAL).
• Fourth-generation reduced user workload and increased computer load, using concise syntax closer to natural language and being user-friendly.
• Fifth-generation languages facilitate alternative architectures, parallel processing, object-oriented approaches, and functional languages like LISP.

Compilers and Interpreters

• Compilers translate high-level programs into machine code, while interpreters execute high-level programs line by line.
• Interpreters may not always produce machine code but instead execute machine code routines to match the high-level instructions.
• Both compilers and interpreters are complex programs and must be written for each language on different computers.
• Compilers translate source code, detect errors, organize storage, and link to other software.
• Compilers allow programs to be used repeatedly after translation, unlike interpreters, with a 1 time translation.
• Compiled programs run faster than interpreted ones because each line is translated only once since interpreters translate each line during each round of a loop.
• Source programs remain stored when interpreters are used which can be an advantage over compilers.
• Programs can be easily changed when a run is unsatisfactory and a high-level program version is shorter than its machine code equivalent.

Computer Programming Tasks include

• Problem definition
• Algorithm generation includes programming language selection
• Coding
• Testing
• Debugging
• Deployment
• Source code maintenance

Qualities of Good Software

• Reliability is how accurate the results of the program are
• Correctness of algorithm
• Usability: Programs should be easy to use for their planned use.
• Portability refers to the range of computer hardware and OS platforms for compiling/interpreting code.
• Maintainability refers to the ease with which a program can be modified by current or future developers.
• Efficiency refers to how much time and memory is needed to finish a computation task in comparison to similar programs.
• Good code is well-indented, and makes use of comments and naming conventions of variables, functions, procedures and classes

Factors in Choosing a Programming Language

• Company policy
• Task Suitability
• Third-party packages Available
• Expertise of the available human resource

Basic Programming Instructions

• Input instructions take data from devices like keyboard, file, etc.
• Output instructions display data on the screen or send data to a file/device.
• Arithmetic instructions perform basic calculations.
• Conditional execution checks conditions and runs code accordingly.
• Repetition repeats actions, potentially with variations.

Explore the basics of computer programming, including instructions, sequence, and pattern types. Learn how instructions dictate computing tasks and understand the BODMAS rule. Discover how programmers write human-readable source code.