Introduction to Programming Languages: Compilers and Language Processing Systems, Lecture notes of Computer Science

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Lecture 1: Introduction

BY: Assist Prof. Dr. Ielaf O Abdul Majjed 2022-

Programming Languages

Hierarchy of Programming Languages based on increasing machine independence includes the following: 1- Machine languages. is the lowest form of computer. Each instruction in program is represented by numeric code, and numerical addresses are used throughout the program to refer to memory location in the computers memory. 2- Assembly languages. is essentially symbolic version of machine level language, each operation code is given a symbolic code such ADD for addition and MULT for multiplication. 3- High level or user oriented languages. such as Pascal, C. 4- Problem oriented language. provides for the expression of problems in specific application or problem area .examples of such as languages are SQL for database retrieval application problem oriented language. Language Processing System Any computer system is made of hardware and software. The hardware understands a language, which humans cannot understand. So we write programs in high-level language, which is easier for us to understand and remember. These programs are then fed into a series of tools and OS components to get the desired code that can be used by the machine. This is known as Language Processing System.

Let us first understand how a program, using C compiler, is executed on a host machine. 1. User writes a program in C language (High-Level Language). 2. The C compiler compiles the program and translates it to assembly program (Low-Level Language). 3. An Assembler then translates the assembly program into machine code (object). 4. A Linker tool is used to link all the parts of the program together for execution (Executable Machine Code). 5. A Loader loads all of them into memory and then the program is executed. Before getting into compilers, we should know a few additional tools. Interpreter Similar to a compiler, an interpreter converts high-level language into machine language. The method by which they read the input or source code differs. A compiler reads the entire source code at once, generates intermediate code, checks semantics, runs the entire program, and may entail multiple passes. A statement is received from the input by an interpreter , which then translates it to intermediate code, executes it, and then reads the next statement in the sequence. An interpreter halts execution and logs errors if they happen. A compiler, however, reads the entire program even if it comes across multiple errors. Assembler An assembler converts programs written in assembly language into machine code. The product of an assembler is referred to as an object file, which combines machine instructions with the information needed to store these instructions in memory.

Linker linker is a computer program that links and merges various object files together in order to make an executable file. The major task of a linker is to determine the memory location where these files will be loaded. Loader Loader is a part of operating system and is responsible for loading executable files into memory and executes them. It calculates the size of a program (instructions and data) and creates memory space for it. A Compiler is a software that typically takes a high level language (Like C++ and Java) code as input and converts the input to a lower level language at once. It lists all the errors if the input code does not follow the rules of its language. A compiler translates the code written in one language to some other language without changing the meaning of the program. It is also expected that a compiler should make the target code efficient and optimized in terms of time and space. A program which is input to the compiler is called a Source program. This program is now converted to a machine level language by a compiler is known as the Object code. Error Messages

Synthesis Phase : Equivalent target program is created from the intermediate representation. It has two parts :

• (^) Code Optimizer
• (^) Code Generator Code Optimizer optimizes the abstract code, and the final Code Generator translates abstract intermediate code into specific machine instructions.