A+B using C++ language
48 bytes
How about...
#include&lt;cstdlib&gt;
main(){system(&quot;tr \\  +|bc&quot;);}

...not using C++?


The call to system runs commands on your shell (&lt;cstdlib&gt; declares system).
tr \\  + executes the command tr, translating spaces to + (so the input34 45 becomes 34+45).
| pipes tr's STDOUT into bc's STDIN.
bc performs equations in STDIN and prints the result to STDOUT.