CODEWITHSUNDEEP
java
Emily Watson
Emily Watson

Reputation: 87

Postdecrement Operations in While loop

b = 5;
    loopiterations = 0;
    while (b-- > 0) {  // Use a postfix decrement
        loopiterations++;         
    }
    System.out.println("Postfix decrement operator used, loopiterations = " +
            loopiterations + ", b = " + b);

The result is

Postfix decrement operator used, loopiterations = 5, b = -1

I don't understand why the value of b is -1. The value of b starts from 5 (after while loop it's value is 4) and then ends at 1 ( after the while loop it is 0) and then the iteration from 5 to 1 is 5.If how I think is right, why is the value of b is -1 after looping. Thank you.

Upvotes: 5

Views: 316

Answers (3)

dreamcrash
dreamcrash

Reputation: 51433

This block of code

   while (b-- > 0) {
      // do something
   }

is semantically the same as

while (b > 0) {
  b--;
  // do something
}
b--;

The loop while (b-- > 0) exits as soon as b == 0, but because of the post decrement operation b will be one last time decrement and hence b will have the value of -1 when printing.

Upvotes: 3

Mahendra Suthar
Mahendra Suthar

Reputation: 131


**postfix increment or decrement actually happens after using value**,
the initial value of b is 5 so in the first iteration 5 is checked for condition after the last iteration, b becomes 0 after its value (1 at time of comparison) has been decremented, then 0 is checked but the condition is false but due to postfix decrement it's value becomes -1.

postfix -> first use value then decrement or increment that's how it works

Upvotes: 2

Koen
Koen

Reputation: 155

This is because when b == 0, the postfix will return false and your while loop will terminate. However, the postifx will still subtract one from b. Therefore, the loop is executed 5 times, and iterations = 5. However, b is decremented 6 times.

Upvotes: 1

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