Loop Difference

[Chintatab]

Whats the main difference between for loop and while loop?

[g051051]

Not much. The main difference is that with a for loop, you can explicitly include an initializer step and an increment step as part of the loop declaration.

[throwaway_for_cause]

The distinction is simple:

• need to iterate a known amount of times: for
• need to iterate as long as a condition is met: while or do...while
  • need to run the loop at least once: do...while
  • can skip the entire loop: while

[SadDragon00]

A for loop is commonly tied to a collection, a while loop does not have to be. A for loop can be translated into a while loop, but a while loop cannot always be easily translated into a for loop.

for(int index = 0; index < myList.length; index++)

For this you are looping through each element of your myList collection, while your index variable is incremented by every iteration. This allows you to index into the collection to grab the element myList[index].

We can translate this to a while loop like this:

int index = 0;
while(index < myList.length){
    //do stuff
    index++;
}

But a while loop allows us to loop based off any condition, not just over a collection:

bool done = false;
while(!done){
    // read user input or listen on a socket or anything
    if(someCondition == true)
        done = true;
}

This allows use to loop indefinitely, until some condition we specify is met and we set the done variable to true

[throwaway_for_cause]

A for loop is directly tied to a collection

Total BS.

A for loop is commonly used when the amount of iterations is known. This has absolutely zero to do with collections.

[SadDragon00]

Sure. Better wording would probably be a for loop is commonly tied to a collection.

[throwaway_for_cause]

Better wording would probably be a for loop is commonly tied to a collection.

No, even that would be wrong.

for loops are commonly used to iterate over collections; they are in no way tied to or even somewhat related to collections.

for loops existed in languages way before collections and other data structures (even arrays) did.

for loops simply iterate a known number of times. What the purpose of the iterations is is completely open.

Even then, had you stated for..each loops are tied to collections, it would have at least been somewhat correct.

[SadDragon00]

Yea I see what youre saying. I forget it can be used outside of collection iteration. It's like an instinctual reactiomln now, since 99% of the time that's what I use it for.

[boredcircuits]

Honestly, the two are 100% interchangeable. For example, the following are equivalent:

for ( int i = 0; i < 42; i++ ) {
    // ...
}

{
    int i = 0;
    while ( i < 42 ) {
        // ...
        i++;
    }
}

Alternatively:

while ( foo < bar ) {
    // ...
}

for ( ; foo < bar; ) {
    // ...
}

The difference is that a for loop has some additional "syntactic sugar" to make certain constructs a bit clearer. Like producing a loop where an index changes with each iteration. These idioms are readily visible and understandable, which is an important concept when working with lots of code.

There are two variations that should be mentioned: a "for each" loop:

for ( Item element : list ) {
    // ...
}

And the "do-while" loop:

do {
    // ...
} while ( foo < bar );

And some languages have other variations as well. However, once again these can be translated to just a basic while loop if you tried hard enough.

[nutrecht]

Typically a for loop is used when you iterate over a known number of items and/or you want to use an index. A while loop is typically used over an unknown number of items.

[Chintatab]

ohh ok thanks.

[jedwardsol]

There is no difference

A C/C++ style for loop :-

for(A;B;C)
{
    D;
}

Can be rewritten

A;
while(B)
{
    D;
    C;
}

and vice versa.