about the possibilities with for loop(+Random function)

Are the following for loops valid?

pawn Code:

for(new i=1;i<10;i*=2)

for(new i=100;i>10;i/=2)

for(new i=25;i>1;i%=10)

Also another doubt is,if i assign a value random(5) to a variable n make it print the number when i execute a command. If i try the command 5 times in a row, will i get completely different numbers all the time (like 1 4 2 3 0) or will any number get repeated (like 4 0 2 4 1)?