what is this loop equivalent to in C++ / C language ? 

 

2)

what is this in reverse engineering 

mov edx, [eax+4]

or

mov edx, [eax] 

I suggest you to learn assembly language. Nobody will explain to you all the ASM syntax in a forum.

Read this one:

https://www.amazon.com/Art-Assembly-Language-Randall-Hyde/dp/1593272073/ref=sr_1_4?s=books&ie=UTF8&qid=1474894924&sr=1-4&keywords=assembly

Or start with lena151 tutorials:

https://tuts4you.com/download.php?list.17

To reply to your question:

mov edx, [eax] 

When the instruction mov edx, [eax] is executed EDX will contain the DWORD at the address pointed by EAX.

According to the picture you posted you're using IDA for disassembling,If I'm not mistaken you could just use 'F5' (if you have IDA with HexRey of course) to show code of that assembly.

for exemple:

 

 

int i = 36;
char *c = [eax+0x124]
while(i-- >0)
{
  *c++=0;
}