Program

What is a program?

• A set of instructions that execute on computer to perform a particular task
• Instructions that run on CPU are in machine code
• instructions that are encoded in binary (1s and 0s)
• Human can not understand machine code directly 
• But human can write programs in machine code
• A tedious, time consuming and very error prone task
• Need computer programming languages –to write a human readable code (source code) which can be converted into machine code

Solution

• Assembly Languages 
• Sets of binary digits are replaced by mnemonics (ADD, MOV)
• Not user friendly, but easier than machine code
• It is hard to understand another person’s assembly language programs
• Assembler: translates mnemonics into machine code
• Assembly languages are second generation languages
• Machine code and Assembly languages are low-level programming languages
• Programming in low-level languages required expertise in the field 
• High level programming languages allow to write programs in English-like symbols 
• write algorithms in a human-friendly notation
• allow thinking at a higher level of abstraction than assembly or machine language supports
• Third generation languages
• Need to convert code in high level languages into machine code 
• Compiler
• translates the whole source code in to machine code at once
• checks syntax errors 
• produces an executable machine code (Machine dependent)
• C, C++ , Java
• Interpreter 
• convert the source code of a program line by line to machine coed while the program is running
• Compilers VS Interpreters
• Compiler produces machine dependent MC at once 
• Interpreter executes source code line by line in every execution of the program 
• Compiler produces optimize MC that run faster on hardware 
• Interpreter might execute a program slower than the compiled machine code for the same program 
• It is easy to point out errors in a program with an Interpreter (Easy to debug)