C
- Modified I/O sample from kattis help pages 
#include <stdio.h>
int main(void) {
    char str[1000];
    while (fgets(str, 1000, stdin)) { //Or scanf
        printf("%s", &str);
    }
    return 0;
}
C++
- Language Reference
- Modified I/O sample from kattis help pages
#include <iostream>
int main(void) {
    long long data;
    while (std::cin >> data)
        std::cout << data << std::endl;
    return 0;
}
Java
- Official Java Documentation
- Unofficial Java reference
- I/O sample from kattis help pages
import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNextLong()) {
            long data = sc.nextLong();
            System.out.println(data);
        }
    }
}
JavaScript (NodeJs)
- I/O sample from kattis help pages 
const readline = require('readline');
const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout
});
rl.on('line', (line) => {
    let data = parseInt(line);
    console.log(data);
});
Octave
- Language reference
- Solution to simple problem.
[name,count,read,err]=scanf("%s %d","C");
for j =  1:count(1,1)
  printf("Hipp hipp hurra, %s!\n", name);
endfor
Python
- Local mirror of python documentation
- I/O sample from kattis help pages
#! /usr/bin/python3
import sys
for line in sys.stdin:
    data = int(line)
    print(data)
Racket
- If you use - racketfor programming contests, you should use- #lang racket, not one of the teaching languages.
- For language reference, run - raco docfrom the command line.
- Sample solution to a slightly more complicated problem. This one has formatted output and reading individual lines of input. 
- Code snippets showing input/output in racket 
#lang racket
;; read stdin line by line, and output each line uppercased with a
;; line number
(define (upcase-stdin)
  (for ([line (in-lines (current-input-port))]
        [count (in-naturals)])
    (printf "~a: ~a~n" count (string-upcase line))))
;; read stdin into a list of numbers, return the list
(define (read-numbers)
  (for/list ([line (in-lines (current-input-port))])
    (string->number line)))
;; read stdin line by line, splitting into words.
(define (read-words)
  (for/list ([line (in-lines (current-input-port))])
    (string-split line)))