Fundamentals of a Program

Basics

• An algorithm is the approach or method used to solve a problem.

• A program comprises statements that solve a specific problem.

• The set of instructions implementing the algorithm constitutes the program.

• Writing a program involves expressing these instructions in a specific computer language, such as Java, C++, Objective-C, or C.

Terminology

• CPU (Central Processing Unit): Performs the majority of computing work, executing instructions.

• RAM (Random Access Memory): Temporarily stores a program's data during runtime.

• Hard Drive (Permanent Storage): Stores program source code files even when the computer is off.

• Operating System: Manages computer resources, handles program execution, and facilitates user interactions (e.g., Windows, Unix, Android).

• Fetch/Execute Cycle: The life cycle of a CPU, where it fetches instructions from memory and executes them.

Learn more about Systems Architecture on BBC Bitesize.

Fetch/Execute Cycle

The fetch-execute cycle, or fetch-decode-execute cycle, is a processor's method for processing instructions. The cycle involves several stages:

1. The memory address in the program counter (PC) is copied into the Memory Address Register (MAR).

2. The program counter's address is incremented by one.

3. The processor sends a signal along the address bus to the MAR.

4. The instruction/data from that memory address is sent along the data bus to the Memory Buffer Register/Data Register (MBR/MDR).

5. The instruction/data in the MBR/MDR is copied into the Current Instruction Register (CIR).

6. The CIR's instruction/data is decoded and executed, with results stored in the Accumulator (ACC).

7. The cycle returns to step one.

Higher Level Programming Languages

• High-level programming languages simplify program writing, providing a more abstract representation of actions.

• Examples include C, offering statements resembling problem-solving steps.

• High-level languages are easier to learn and program in than machine languages.

• Compilers translate high-level language source code into detailed machine language instructions, handling syntax checking.

Steps in Writing a Program

1. Define Program Objectives:

   • Understand program requirements and objectives clearly.

2. Design:

   • Plan how the program will meet the defined requirements.

   • Consider user interface and program organization.

3. Write the Code:

   • Begin implementation by translating the design into C syntax.

   • Create a source code file using a text editor.

4. Compile:

   • Translate the source code into machine code, forming an executable file with CPU instructions.

5. Run the Program:

   • Execute the program using the generated executable file.

6. Test and Debug:

   • Test the program to ensure it functions as intended.

   • Debugging involves finding and fixing errors.

7. Maintain and Modify the Program:

   • Continue fixing bugs and adding features as needed.

   • Iteratively go through steps based on evolving requirements.

For effective development, consider jumping between steps and repeating them as necessary.