php reading files and moving down lines

[hargi]

oh i can get php to read from a text file.
what i want to do now is put the first line into a variable then the second line in to a second variable. check something then make the first variable the same as the 3rd line
Psedo code
Variable 1 = first line
Variable 2 = second line
"do something"
clear variable 1 and 2
Variable 1 = third line
varible 2 = forth line
ect repeat till end of file.

 

[hargi]

that works a treat, is there a way of instead of putting
$line3
$line4 ect for each one of the lines.
as i dont know how many lines there will be
getting it to automatically create the smae amount of line variables as there is lines in the text.

 

[hargi]

cheers rob that works for the
$lines[$i]
but if i try to

echo "$lines[$i + 1]";

i get
Parse error: syntax error, unexpected T_ENCAPSED_AND_WHITESPACE, expecting ']' in C:\xampplite\htdocs\passwordsite\read.php on line 14
i tried getting rid of the spaces or putting in [$i+[1]] and other variations but still get same result

 

[hargi]

thanks
whats the rules with when to use " " and when not to