my issue is that how can i program multiple pins to be set as an output without the need of writting, pinMode function 100 times
Perhaps a for loop would work. 4 lines of code, instead of 100.
and digitalWrite function 200 times if i want the 100 solenides to be tuned on and then off..
Are you planning on banging all 100 solenoids on and off at the same time? If so, you can do that by connecting them all to the same pin, and use just two statements to turn them all on or off.
If they are to be turned on and off at different times, then you will still have to write all the code to make that happen. No magic bullets.