question about "random" and a calculator

hello all, im new to C++ so sorry if these questions are kind of noob (wich they probably are :D )

im trying to learn C++ by folowing the tutorials at this site, and so far it works pretty good.

but after doing lesson 1 (or 2 maybe) i made a really basic calculator, but i cant get it to work fully.

i do not know how to get C++ to use an operator that was put in by the user, so i tried simply NR3= NR1 OP1 NR2 where NR1 is the first input, OP1 the operator input, and NR3 is the second number input.

i have added my complete calculator C++ code.

how would i make this work?

second, i tried at lesson 3 the random option, but i cant get it really random, its semi random, in wich i get the same numbers over and over again.

i know computers aren't really capable of generating random numbers, but i think it should be a litle more random every time i open the program...

i saw the rest of the lesson, im just curious about why it gives me every time the same number sequency...

i have also added that C++ code in this post.

thanks in advance for the answers!