multiple conditions Under the 'for' loop

Question

Why doesn't the conditional Boolean in the standard for loop below behave as expected? I'm trying to get 3 and 4, indexes 2 and 3 in the array below to print out. If I try to specify the range in the condition of the for loop it doesn't run the loop. To test the conditional in an if condition ( see 2nd listing it works )

Why doesn't it simply work just in the for loop ?

int[]weather = {1,2,3,4,5,6,7};
for(int i=0;i>1&&i<4; i++ ) {
    //if(i>1&&i<4) {
        System.out.println("Weather is ===> "+weather[i]);
    //}
}

nothing printed...

int[]weather = {1,2,3,4,5,6,7};
for(int i=0;i<10; i++ ) {
    if(i>1&&i<4) {
        System.out.println("Weather is ===> "+weather[i]);
    }
}

Weather is ===> 3
Weather is ===> 4

Because 0 is less than 1 so the loop condition is already false on the first iteration? — UnholySheep, Sep 09 '21 at 12:45
"`for(int i=0;i>1&&i<4; i++ ) {`" the condition is immediately false. — Andy Turner, Sep 09 '21 at 12:45
Note that the condition in a loop is used to check whether it should continue running (or start at all) and if the first check returns false (because 0 > 1 is false) it never starts. If that weren't the case, how should the loop "know" when to stop? — Thomas, Sep 09 '21 at 12:49

score 1 · Answer 1 · answered Sep 09 '21 at 12:49

1

for(int i=0;i>1&&i<4; i++ ) dosen't work because since i=0 and it dosen't satisfy the condition in a loop and thus the program never enters the loop.

This is usually used to sometime skip the loop when not needed.

answered Sep 09 '21 at 12:49

bartick maiti

178
9

score 0 · Accepted Answer · answered Sep 09 '21 at 12:47

0

for(int i=0;i>1&&i<4; i++ ) {
            ^------^ expression

For loops execute until the expression is false, and then stop executing. This expression is immediately false (because 0>1 is false), so it immediately stops executing. It doesn't "wait and see" if the expression becomes true again.

If you only want the loop to execute for i>1&&i<4:

for(int i = 2; i<4; i++ ) {

answered Sep 09 '21 at 12:47

Andy Turner

137,514
11
162
243

Thanks.. for some reason I forgot the fact that the loop stops, shuts down immediately upon 1st false. That the conditional meant stop running. – JohnnyO Sep 09 '21 at 13:24

score 0 · Answer 3 · answered Sep 09 '21 at 12:48

Simply you don't pass the condition after the initialization. At the beginning i is set to 0. The loop continues until i is between 1 and 4 (both excluded), so you never start the loop.

for (int i = 0; i > 1 && i < 4; i++) {
    // You never goes here because i is 0 so not > than 1
    ...
}

Instead if you put the condition inside the loop you bypass execute all the iterations and for some of them you enter the if condition.

multiple conditions Under the 'for' loop

3 Answers3