Which loop to use, for or do/while?

Question

Using C# (or VB.NET) which loop (for loop or do/while loop) should be used when a counter is required?

Does it make a difference if the loop should only iterate a set number of times or through a set range?

Scenario A - The for loop

for (int iLoop = 0; iLoop < int.MaxValue; iLoop++)
{
  //Maybe do work here

  //Test criteria
  if (Criteria)
  {
    //Exit the loop
    break;
  }

  //Maybe do work here
}

Advantages

• Counter is declared as part of loop
• Easy to implement counter range

Disadvantages

• Have to use an if to leave the loop

Scenario B - The do/while loop

int iLoop = 0;
do
{
  //Increment the counter
  iLoop++;

  //Do work here
} while (Criteria);

or

int iLoop = 0;
while (Criteria)
{
  //Increment the counter
  iLoop++; 

  //Do work here 
}

Advantages

• Leaving the loop is part of the loop structure
• Choice to evaluate before or after loop block

Disadvantages

• Have to manage the counter manually

Answer 1

I ususually use for, cause it's simple. I use while when counter is needed after or before loop or if using for is impossible.

Answer 2

How about the best of both worlds:

for (int iLoop = 0; iLoop < int.MaxValue && !Criteria; iLoop++)

Edit: Now that I think about it, I suppose comparing against int.MaxValue wasn't part of the criteria, but something to emulate an endless for loop, in that case you could just use:

for (int iLoop = 0; !Criterea; iLoop++)

Answer 3

At least for me i use for() when i need to traverse an array and when no breaking is needed. And do() and while() when i need to process something for an unknown time.

Answer 4

You can always add the exit criteria to for loop:

for (int iLoop = 0; iLoop < int.MaxValue && Criteria; iLoop++)
{
  //Maybe do work here
}

I would really go for whatever looks most readable in your particular case.

Answer 5

for (int iLoop = 0; iLoop < int.MaxValue && !Criteria; iLoop++) {
    //Do work here...
}

Answer 6

There's no reason not to use a for loop in this case. Even if you have other criteria, it's perfectly valid to write:

for (int iLoop = 0; iLoop < int.MaxValue && Criteria; iLoop++) { ... }

Answer 7

Personally I would go with the for loop.

It is better to read, more commonly used and very optimized.

for (int iLoop = 0; iLoop < int.MaxValue && !Criteria; iLoop++)
{
// Do Work
}

Edit: int.MaxValue && !Criteria <- a definietely better approach than my initial one ;)

Answer 8

for loops consist of the following:

for ( initialization; condition; action )

you don’t need an extra if to check your criteria, what do you think is i < value? it’s nothing more than a criteria.

i use loops when they fit the problem, there’s no definite answer

Answer 9

Just for completeness, you could also use option D:

for (int iLoop = 0; Criteria; iLoop++)
{
   // work here
}

(where Criteria is "to keep running")

the condition in a for loop doesn't have to involve iLoop. Unusual, though, but quite cute - only evaluates before work, though.

Answer 10

Instead of a dummy criteria in the for loop, you can use the actual criteria that you want to use for the loop:

Scenario A2 - the for loop with custom criteria:

for (int iLoop = 0; Criteria; iLoop++) {

  // do work here

}

This is equivalent to:

{
   int iLoop = 0;
   while (Criteria) {

      // do work here

      iLoop++;
   }
}

If you have a loop counter, you should generally use a for loop to make that clearer.

Answer 11

Write some test cases and see which works best for you. Have a look a this link: .Net/C# Loop Performance Test (FOR, FOREACH, LINQ, & Lambda)

Answer 12

I'd tend to use for if I'm actually using the counter in the loop, say as an index into an array, and as part of the criteria, i.e. "stop at the end of the array" rather than "just don't overflow".

If I'm looping over something with unknown length, such as lines in a file, or just maintaining the counter to use the total after the loop, then I'll use do or while.

However, it really comes down to what's more readable for a particular situation. I expect that you'd struggle to tell from the compiled IL which version was used.

Answer 13

((((difference b/w while and do while--> let me tell you with one example : if a person going into a hall to fix a bomb inside the hall, he must be checked when getting in.. in another case if a person going into a hall to steal something from there he must have been checked when coming out of the hall.. so based on the process only we have to use our looping condition....))))

The for loop can execute a block of code for a fixed or given number of times.if your counter variable depends on that block of code(means inside the looping condition), you can use the for loop