compilers and interpreters compilers and interpreters These are

compilers and interpreters

compilers and interpreters • These are programs which translate computer programs from high-level languages such as Pascal, C++, Java or Java. Script into the raw 1 s and 0 s which the computer can understand, but the human programmers cannot:

compilers and interpreters • You write this The computer translates it . . . into this, which it can run

compilers and interpreters • Compilers were the first sort of translator program to be written. • The idea is simple: You write the program, then hand it to the compiler which translates it. Then you run the result. • The compiler takes the file that you have written and produces another file from it. • The compiler has another task apart from translating your program. • It also checks it to make sure that it is grammatically correct. • Only when it is sure that there are no grammatical errors does it do the translation. • Any errors that the compiler detects are called compile-time errors or syntax errors. • If it finds so much as one syntax error, it stops compiling and reports the error to you.

compilers and interpreters • Interpreters • An interpreter is also a program that translates a high-level language into a low-level one, but it does it at the moment the program is run. • You write the program using a text editor or something similar, and then instruct the interpreter to run the program. • It takes the program, one line at a time, and translates each line before running it: • It translates the first line and runs it, then translates the second line and runs it etc. • The interpreter has no "memory" for the translated lines, so if it comes across lines of the program within a loop, it must translate them afresh every time that particular line runs. • Consider this simple Basic program: • 10 FOR COUNT = 1 TO 1000 • 20 PRINT COUNT * COUNT • 30 NEXT COUNT

compilers and interpreters • Line 20 of the program displays the square of the value stored in COUNT and this line has to be carried out 1000 times. • The interpreter must also translate that line 1000 times, which is clearly an inefficient process. • Examples of interpreted languages are Basic, Java. Script and LISP.

Diff compilers and interpreters • We usually prefer to write computer programs in languages we understand rather than in machine language, but the processor can only understand machine language. • So we need a way of converting our instructions (source code) into machine language. • This is done by an interpreter or a compiler. • An interpreter reads the source code one instruction or line at a time, converts this line into machine code and executes it. • The machine code is then discarded and the next line is read. • The advantage of this is it's simple and you can interrupt it while it is running, change the program and either continue or start again. • The disadvantage is that every line has to be translated every time it is executed, even if it is executed many times as the program runs. • Because of this interpreters tend to be slow.

Diff compilers and interpreters • A compiler reads the whole source code and translates it into a complete machine code program to perform the required tasks which is output as a new file. • This completely separates the source code from the executable file. • The biggest advantage of this is that the translation is done once only. • The program that is run is already translated into machine code so is much faster in execution. • The disadvantage is that you cannot change the program without going back to the original source code, editing that and recompiling.

compilers and interpreters