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Nim Basics — Syntax, Variables, Types, and Compilation

DodaTech Updated 2026-06-29 2 min read

In this tutorial, you will learn about Nim Basics. We cover key concepts, practical examples, and best practices to help you master this topic.

Nim is a systems programming language that combines Python's readability with C's performance. It compiles to C, C++, or JavaScript, giving you low-level control without sacrificing expressiveness.

In this tutorial, you'll learn Nim's core syntax and execution model. Nim is used at DodaTech for performance-critical security tools where Python is too slow but C is too verbose.

What You'll Learn

  • Installing Nim and compiling programs
  • Variables and type inference
  • Basic types
  • Compilation modes (debug, release)
  • Input and output

Hello, Nim

echo "Hello, Nim!"

# Compile and run:
# nim c hello.nim && ./hello

Variables

# Immutable by default (let)
let name = "Alice"
# name = "Bob"  # Error: cannot assign to let

# Mutable variables (var)
var age = 30
age = 31  # OK

# Explicit types
let country: string = "India"
var count: int = 0
let pi: float64 = 3.14159

Basic Types

# Integers
let
  a: int8 = 127
  b: int16 = 32767
  c: int32 = 2147483647
  d: int64 = 9223372036854775807
  e: uint = 42       # Unsigned

# Floats
let
  f: float32 = 1.5
  g: float64 = 3.141592653589793

# Characters and strings
let
  ch: char = 'A'
  s: string = "Hello"
  multi = """Multi-line
string"""

# Booleans
let
  flag: bool = true
  another = false

# Type conversions
int("42")      # => 42
float(3)       # => 3.0
$42            # => "42" (stringify)

Control Flow

# if/elif/else
let score = 85
let grade = if score >= 90:
  "A"
elif score >= 80:
  "B"
else:
  "F"
echo grade  # B

# case
let status = case score:
  of 90..100: "Excellent"
  of 80..89:  "Good"
  of 70..79:  "Fair"
  else:       "Needs improvement"

# loops
for i in 0..4:
  echo i  # 0, 1, 2, 3, 4

for item in ["Alice", "Bob", "Charlie"]:
  echo item

var i = 0
while i < 5:
  echo i
  inc i

Procedures

# Functions are called procedures
proc add(a, b: int): int =
  return a + b

# Implicit return (last expression)
proc multiply(a, b: int): int =
  a * b

# Default arguments
proc greet(name: string = "World"): string =
  "Hello, " & name & "!"

echo greet()        # Hello, World!
echo greet("Nim")   # Hello, Nim!

# Multiple return values
proc divide(a, b: int): (int, int) =
  (a div b, a mod b)

let (q, r) = divide(10, 3)
echo q  # 3
echo r  # 1

Compilation

# Debug build (fast compilation, slow execution)
nim c hello.nim

# Release build (slow compilation, fast execution)
nim c -d:release hello.nim

# Run without producing binary
nim r hello.nim

# Compile to JavaScript
nim js hello.nim

Practice Questions

  1. Write a procedure that takes two integers and returns their sum, difference, and product.

  2. Use a for loop to print the first 20 Fibonacci numbers.

  3. Write a case statement that categorizes an integer as single-digit, double-digit, or triple-digit.

  4. Create a procedure with a default parameter value.

  5. Write a program that reads a name from stdin and prints a greeting.

← Previous Nim: Fast, Expressive Systems Programming Next → Nim Data Types — Strings, Arrays, Sequences, Sets, and Tables

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