What is the difference between a compiler and an interpreter?

When you write code in a compiled language (like C++ or Rust), you run a special program called a compiler. The compiler reads every single line of your source code and translates the whole thing into a new file of machine code (binary). This creates an executable file (like a .exe on Windows). Because all the translating is done ahead of time, the final program runs very fast. However, if you make a tiny change to your code, you have to recompile the entire program before you can see the change.

When you write code in an interpreted language (like Python or JavaScript), there is no separate step to build an executable file. Instead, you just run the code. The interpreter software looks at the first line of your code, translates it into machine instructions, and runs it immediately. Then it moves to the second line. Because it translates on the fly, interpreted code usually runs slower than compiled code. But it is much faster for developers to test and debug, because you don't have to wait for a compiler to process the whole file.

A common mistake is assuming that a programming language is strictly one or the other. In reality, compiling and interpreting are just ways to execute code. While C is almost always compiled and JavaScript is almost always interpreted, many modern languages use a hybrid approach. For example, Java compiles your code into an intermediate format called "bytecode." Then, a Java interpreter (the Java Virtual Machine) runs that bytecode. Python does this behind the scenes, too!