A+B is one of the most complex problems on this website due to its large variety of solutions.

C

    1 #include<stdio.h>
    2 
    3 int main(void) {
    4 	int a, b;
    5 	scanf("%d%d", &a, &b);
    6 	printf("%d", a + b);
    7 	return 0;
    8 }

C++

    1 #include<iostream>
    2 
    3 int main(void){
    4 	int a, b;
    5 	std::cin >> a >> b;
    6 	std::cout << a + b;
    7 	return 0;
    8 }

D

    1 import std.stdio;
    2 
    3 void main(){
    4     long a, b;
    5     readf("%d %d", &a, &b);
    6     writeln(a+b);
    7 }

Go

    1 package main
    2 import "fmt"
    3 
    4 func main() {
    5 	var a, b int
    6 	fmt.Scanf("%d%d", &a, &b)
    7 	fmt.Print(a + b)
    8 }

GolfScript

    1 ~+

Haskell

    1 import Control.Applicative
    2 
    3 main :: IO ()
    4 main = do
    5         [ a, b ] <- map read . words <$> getLine
    6         print (a + b :: Int)

Java

In Java, the class must be named prog.

    1 public class prog {
    2 	public static void main(final String[] args) {
    3 		java.util.Scanner scan = new java.util.Scanner(System.in);
    4 		System.out.println(scan.nextInt() + scan.nextInt());
    5 	}
    6 }

Oberon

    1 MODULE prog;
    2 
    3 IMPORT In, Out;
    4 
    5 VAR a, b : INTEGER;
    6 
    7 BEGIN
    8   In.Int(a);
    9   In.Int(b);
   10   Out.Int(a + b, 0);
   11   Out.Ln
   12 END prog.

OCaml

    1 let sum a b = a + b
    2 
    3 let _=
    4     Printf.printf "%i\n" ((Scanf.scanf "%i %i" sum))

Pascal

    1 var a,b:integer;
    2 begin
    3 read(a,b);
    4 write(a+b);
    5 end.

Perl

    1 #!/usr/bin/perl
    2 use v5.14;
    3 use warnings;
    4 
    5 my ($x, $y) = split ' ', <>;
    6 say $x + $y;

PHP

    1 <?php
    2 fscanf(STDIN, "%d %d\n", $a, $b);
    3 echo $a+$b . "\n";
    4 ?>

Python

    1 #!/usr/bin/python
    2 print sum(map(int, raw_input().split()))

Python3

    1 #!/usr/bin/python3
    2 print(sum(map(int, input().split())))

Ruby

    1 p gets.split(' ').map(&:to_i).inject 0, :+

Rust

    1 use std::io;
    2 
    3 fn main() {
    4     let mut input = String::new();
    5 
    6     let _ = io::stdin().read_line(&mut input);
    7 
    8     let mut sum: i64 = 0;
    9     for x in input.trim().split(" ").collect::<Vec<&str>>() {
   10         sum += match x.parse::<i64>() {
   11             Ok(val) => val,
   12             _       => 0,
   13         };
   14     }
   15 
   16     println!("{}", sum);
   17 }

SBCL

    1 (format t "~d" (+ (read) (read)))