What is the difference between prefix and postfix operators?

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There is a big difference between postfix and prefix versions of ++.

In the prefix version (i.e., ++i), the value of i is incremented, and the value of the expression is the new value of i.

In the postfix version (i.e., i++), the value of i is incremented, but the value of the expression is the original value of i.

Let’s analyze the following code line by line:

int i = 10;   // (1)
int j = ++i;  // (2)
int k = i++;  // (3)
  1. i is set to 10 (easy).
  2. Two things on this line:
    • i is incremented to 11.
    • The new value of i is copied into j. So j now equals 11.
  3. Two things on this line as well:
    • i is incremented to 12.
    • The original value of i (which is 11) is copied into k. So k now equals 11.

So after running the code, i will be 12 but both j and k will be 11.

The same stuff holds for postfix and prefix versions of --.

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