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Dr. Ajay Dutta

Proramming Languages

Programming Language

Language is a set of symbols being used mainly for communication. The symbols may be spoken or written. 










A programming language is a set of grammatical rules for instructing a computer to perform specific tasks.
The term programming language usually refers to high-level languages, such as BASIC, C, C++, COBOL, Java, FORTRAN, Ada, and Pascal.
Each programming language has a unique set of keywords and a special syntax for organizing program instructions.






Machine Language
A computer’s CPU is incapable of speaking C++. The very limited set of instructions that a CPU natively understands is called machine code (or machine language or an instruction set). How these instructions are organized is beyond the scope of this introduction, but it is interesting to note two things. First, each instruction is composed of a number of binary digits, each of which can only be a 0 or a 1. These binary numbers are often called bits (short for binary digit). For example, the MIPS architecture instruction set always has instructions that are 32 bits long. Other architectures (such as the x86, which you are likely using) have instructions that can be a variable length.
Here is an example x86 machine language instruction: 10110000 01100001
Second, each set of binary digits is translated by the CPU into an instruction that tells it to do a very specific job, such as compare these two numbers, or put this number in that memory location. Different types of CPUs will typically have different instruction sets, so instructions that would run on a Pentium 4 would not run on a Macintosh PowerPC based computer. Back when computers were first invented, programmers had to write programs directly in machine language, which was a very difficult and time consuming thing to do.

Assembly Language
Because machine language is so hard to program with, assembly language was invented. In an assembly language, each instruction is identified by a short name (rather than a set of bits), and variables can be identified by names rather than numbers. This makes them much easier to read and write. However, the CPU can not understand assembly language directly. Instead, it must be translated into machine language by using an assembler. Assembly languages tend to be very fast, and assembly is still used today when speed is critical. However, the reason assembly language is so fast is because assembly language is tailored to a particular CPU. Assembly programs written for one CPU will not run on another CPU. Furthermore, assembly languages still require a lot of instructions to do even simple tasks, and are not very human readable.
Here is the same instruction as above in assembly language: mov al, 061h

High-level Languages
To address these concerns, high-level programming languages were developed. C, C++, Pascal, Java, Javascript, and Perl, are all high level languages. High level languages allow the programmer to write programs without having to be as concerned about what kind of computer the program is being run on. Programs written in high level languages must be translated into a form that the CPU can understand before they can be executed. There are two primary ways this is done: compiling and interpreting.

compiler is a program that reads code and produces a stand-alone executable program that the CPU can understand directly. Once your code has been turned into an executable, you do not need the compiler to run the program. 


An interpreter is a program that directly executes your code without compiling it into machine code first. Interpreters tend to be more flexible, but are less efficient when running programs because the interpreting process needs to be done every time the program is run. 


Any language can be compiled or interpreted, however, traditionally languages like C, C++, and Pascal are typically compiled, whereas “scripting” languages like Perl and Javascript are interpreted. Some languages, like Java, use a mix of the two.







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