While循环条件php

Question

Why does not the second example work the same way as the first? Look at the condition of the loop. Is it not exactly the same condition just different ways of writing it?

The first example becomes false when there is nothing more to get. And then it stops. But the second example never becomes false, it keeps filling the screen with results and never gets done. Endless loop.

Why does the examples behave differently and not exactly the same?

//First ex
while ($rows = mysqli_fetch_assoc($query)) {
print_r($rows);
}



//second ex
$rows = mysqli_fetch_assoc($query);
while ($rows) {
print_r($rows);
}

Answer 1

First one will fetching mysql data every loop. Because statement inside condition checking will run each checking. Second one is only run once.

Answer 2

the second while statement has no condition inside while(condition){} right now you have just declared a variable. hence it does not execute in the same manner as the first statement.

Answer 3

//First ex
while ($rows = mysqli_fetch_assoc($query)) {
print_r($rows);
}

This is getting executed at each iteration so putting next value inside $row at each iteration.

//second ex
$rows = mysqli_fetch_assoc($query);
while ($rows) {
print_r($rows);
}

In above code you are putting only first iteration value to $row . $row is not getting updated at each iteration. So this will run forever.

Conclusion :

Each time you call mysqli_fetch_assoc($query) it gives next row.

In first example, $row is having next row at each iteration by calling mysqli_fetch_assoc($query) again and again on every iteration.

Whereas in second example mysqli_fetch_assoc($query) is getting called only once. So your $row will have value every time you run while so it will run for infinite time.

Answer 4

//mysql users table
//id | nick | date
//1    | x1    | 2018-01-05
//2    | x2    | 2018-01-06
//3    | x3    | 2018-01-07

while ($row = mysqli_fetch_assoc($query)) {
    print_r($row);
}

//first loop call row one
//second loop  call row two
//third loop  call row  three

print_r(mysqli_fetch_assoc($query)); //print row one and mysql cursor jump to row two
print_r(mysqli_fetch_assoc($query)); //print row two and mysql cursor jump to row there
print_r(mysqli_fetch_assoc($query)); //print row there

//but mysqli_fetch_assoc bring one row not rows
$row = mysqli_fetch_assoc($query);


//row is null, no print and repeat
//row is null, no print and repeat
//row is null, no print and repeat
//row is null, no print and repeat
// ∞ :))
while ($row) {
    print_r($row);
}