J-Fundamentals

Hello World in J

Every programming journey starts with Hello World. In J, this is remarkably concise—just a string expression that outputs to the screen.

The Code

Create a file named hello.ijs:

1

'Hello, …

Variables and Types in J

In most languages, variables hold single values—a number, a string, a boolean. In J, the fundamental unit of data is the array. Even a single number is an array (a zero-dimensional one). Understanding …

Operators in J

In most programming languages, “operators” are a small, fixed set of infix symbols like +, -, and ==. In J, what other languages call operators are called verbs, and they are first-class …

Control Flow in J

Most languages treat control flow as the backbone of a program: you branch with if, you repeat with for and while, and you walk through data one element at a time. J supports all of these structures, …

Functions in J

In most languages a “function” is a named block of statements that you call with arguments. J has functions too, but it calls them verbs, and the way you build them reflects J’s …

I/O Operations in J

Input and output in J are handled by foreign conjunctions — the !: family of system verbs you first met in Hello World, where 1!:2 (2) wrote a string to the screen. The 1 class is the file/console …