#include <stdio.h>
  
  int main(int argc, char* argv[]){
  	int arr[1];
  	int a = 2;
  	int b = 2;
  	arr[1] = 3;
  	printf("%d", a+b);
  
  	return 0;
  }

    $ cat test.c
    #include <stdio.h>
    
    int main() {
        int a = 3;
        int b = 3;
    
        // aren't we supposed to add 2 and 2 ??/
        a = 2;
        b = 2;
    
        printf("%d\n", a + b);
    
        return 0;
    }
    $ gcc -W -Wall -trigraphs test2.c 2>/dev/null
    $ ./a.out
    5
    $

Edit: I had a feeling I'd heard of an "integer cache" somewhere else" in a WTF-eliciting context... http://thedailywtf.com/Articles/The-Integer-Cache.aspx !

  #include <stdio.h>

  int main() {
    double x;
    printf("Input any number:\n> ");

    if (scanf("%lf", &x) == 1) {
      printf("Is 2 + 2 really equals %g? Let's try!\n", x);
      printf("2 + 2 = %g\n", 2 + 2);
    } else {
      printf("Invalid input!\n");
    }
  }

  Input any number:
  > 5
  Is 2 + 2 really equals 5? Let's try!
  2 + 2 = 5

http://codegolf.stackexchange.com/a/29944/12328

  class Fixnum
    alias_method :old_plus, :+
    def +(*args)
      old_plus(*args).old_plus(1)
    end
  end

  2 + 2 #=> 5

  public class Main {
   	public static void main (String [] args) {
  		System.out.println("‮5=2+2‭"); // prints ‬4=2+2
  	}
  }

    #include <stdio.h>
    #include <stdbool.h>
    #include <stdlib.h>

    int nums[5] = {1, 0, 1, 0, 1};
    static int cur;

    int main(int argc, char **argv) {
        for(int i = 1; nums[i] != 5 && i < 10; i++) {
            cur = i;
            if(i/4 == 1) {
                printf("2 + 2 <= %d = %s\n", cur, 2 + 2 <= i ? "true" : "false");
                printf("2 + 2 == %d = %s\n", cur, 2 + 2 == i ? "true" : "false");
                printf("\n");
            }
        }
    }

It's finicky and I believe depends on register allocation, but when I compile it using whatever version of gcc-mp-4.9 I have installed from MacPorts at -O3, it outputs, among other things:

    2 + 2 == 5 = true

  #include <printf.h>
  #include <stdio.h>
  #include <string.h>

  int d_cb(FILE *stream, const struct printf_info *info, const void *const* args) {
    int num = (*(int*)(((int**)args)[0])), numw = info->width;
    char str[10], numn = num|numw, *out = str;
    num = num < 0 ? *out++ = '-', -num : numn;
    do { *out++ = '0' + num % 10; num /= 10; } while(num);
    fwrite(str, out - str, 1, stream);
    return 0;
  }

  void init() {
    register_printf_function('d', d_cb, 0);
  }

  int main() {
    init();
    printf("2+4 = %d, 2+2 = %1d\n", 2+4, 2+2);
    return 0;
  }

  multi infix:<+>(2, 2) { 5 }
  say 2 + 2;  # 5

  def mad_addr(a,b)
    a == b && a == 2 ? (a.object_id + b.object_id)/a : a + b
  end

I just learned the object_id of 2 is 5 while doing this exercise, and I would like to continue learning more about how Ruby works. So if you have feedback, criticisms, or other ideas regarding this solution please feel free to share :)

[edit: added missing `=`]

    local debug = require "debug" -- in case 5.2
    debug.setmetatable(1, {__tostring=function(n)
      return ("%g"):format(n+1)
    end})

    print(2+2)

    add2And3(int *a, int *b)
    {
       *a = 3;
       *b = 2;
       printf("%d", *a + *b);  //4
    }
    void main()
    {
       int storage;
       add2And3(&storage, &storage);
    }

  #!/bin/bash
  tty
  if [[ $? -ne 0 ]] ; then
      # command returned nonzero
      echo "not a tty"
  else
      # command returned zero
      n=$?
      ((n=$n+2))
      ((n=$n+2))
      echo "0+2+2=$n";
  fi

  let 2 + 2 = 5

   > '%+%' <- get( '+')
   > '+' <- function( e1, e2) 1 %+% e1 %+% e2
   > 2+2
   [1] 5

http://play.golang.org/p/XnPglbkLW4

  (let [+ (partial + 1)]                                                                                                                                                                                
        (+ 2 2))

  !(a::Int) = !bool(a)
  !0 + 2 + 2

  ##> 5

    class A {
        public static void main(String[] args) {
            Integer a = 100, b = 100;
            Integer c = 10000, d = 10000;
            System.out.println(a == b);
            System.out.println(c == d);
        }
    }

    true
    false

Personally I'd just employ an enhancing classload and replace some of bytecodes ICONST_2 with ICONST_3. (one byte change in the bytecode). Yet, overall uninteresting question.

It looks like you are missing an equals sign on a == 2.

I just learned the object_id of 2 is 5 while doing this exercise, and I would like to continue learning more about how Ruby works. So if you have feedback, criticisms, or other ideas regarding this solution please feel free to share :)

The object_id appears to be the tagged pointer that contains the value cast to an integer. Ruby stores all of its data types using a single underlying C data type (called VALUE in the Ruby source), using the bottom two bits to identify special values that aren't really pointers. This is why Fixnum can only hold 31 or 63 bits instead of 32 or 64 (including sign), for example:

    # Ruby irb on a 32-bit system
    > (1<<30 - 1).class
    => Fixnum
    > (1<<30).class
    => Bignum

https://en.wikipedia.org/wiki/Tagged_pointer