Program Structure

• The text provides an introduction to the structure of a program

Objectives of the Study Unit

• Acquire a certain way of reasoning.
• Automate problem-solving strategies.
• Master the concepts of algorithms.
• Learn the process of programming without specializing in one particular language.
• Illustrate the concepts with an imperative language, C.

Introduction

• Memory is a place to store binary data.
• An octet (byte) is a sequence of 8 bits.
• Computers need conventions to represent integers, characters, and real numbers with bits and octets.
• Computers use integers, reals, and characters for predefined data objects.
• The CPU executes machine instructions coded in memory as 0s and 1s.
• A series of instructions forms executable code.
• Executable code is binary machine language recognizable by a CPU.

Programming Languages

• High-level languages express data and instructions abstractly.
• The code produced is independent of the computer's architecture.
• Programming languages include:
• Logical languages program proofs based on axioms and logic rules, describing what should be calculated rather than how (e.g., Prolog, Obj3, Coq).
• Functional languages describe a program as a set of function definitions (e.g., OCaml, Haskell).
• Imperative languages explicitly describe successive instructions for the computer to execute on data in memory (e.g., C, C++, Python, Java, Pascal).
• Programs are sets of instructions written in a programming language.

Compilation vs. Interpretation

• Programs must be compiled or interpreted to be executed.
• Compiled programs are translated into executable machine language by a compiler, readable by the CPU, then executed, for example: C, C++, Pascal.
• Interpreted programs are executed directly via an interpreter (such as Python, OCaml).
• Compiled programs run faster and use fewer resources, while interpreted programs are more portable and can run on any platform with an interpreter.
• Some languages are semi-interpreted (like Java), they are compiled into an intermediate code and executed by a virtual machine, which compiles and executes it on the fly.
• Some languages have compilers and interpreters (Ocaml, Haskell), some are compiled (C, C++), and others are interpreted (Python).
• In this course, the language C is used for its imperative compiled features

Algorithms

• Algorithms are a sequence of operations or instructions to solve a problem or achieve a result such as a cooking recipe or GPS directions.
• A program is a translation of an algorithm into a programming language.
• Algorithms predate computers and can calculate the greatest common divisor (GCD), sort lists, or schedule tasks.
• Al-Khwarizmi, a mathematician from Baghdad around the year 800 known for math, also contributed to naming algorithms; also arithmos which gave arithmetic.
• Programs describe algorithms, but algorithms do not depend on the language.
• Algorithms can be written in natural language, represented by a diagram, or given as a mathematical formula.
• An algorithm's characteristics involve:
• Inputting a finite number of data.
• Defining each step rigorously and unambiguously.
• Terminating and providing a result.
• Being deterministic: it must produce the same result with the same input.

Analyst-Programmer Role

• The production chain for an executable program: problem analysis,algorithm design, programming, compilation or interpretation, producing a result.

Programs in C

• A programming language involves rules, grammar, and precise syntax.

Basics of Imperative Programming and the C Language

• An imperative program contains:
• Descriptions of non-elementary types.
• Instructions describing operations in order.
• Combinations of instructions (repetitions, conditionals).
• Instructions in a specific order.

Structure of a C Program

• C programs must be written in a text file, edited, saved with the ".c" extension.
• In C, a program's structure follows this order:
• Preprocessor directives replaced during compilation, such as #include <stdio.h>.
• Definitions of non-elementary types.
• Definitions of functions.
• Only one function is named main where the program execution starts and is mandatory.
• Type definitions are global and usable in all functions.
• Comments:
• Can be added to provide context.
• Are ignored by the compiler
• Can be enclosed between /* and */ for multiple lines
• Use // for single-line comments.
• Comments improve code reusability.

Compilation

• Compile C programs with the command "gcc filename.c -o executable_name", for example, gcc addition.c -o addition.
• Integrated Development Environments (IDEs) include text editors with syntax highlighting and functions for compilation, execution, and debugging.