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Increment & decrement operators: ++ & --

The increment ++ and decrement -- operators increase or decrease the value of the operand by one.

There are two ways we can use them:

  • Prefix: The operand value is incremented by one, then the new value is returned.
  • Postfix: The original value of the operand is returned, then the operand is incremented by 1.

Postfix​

When we use the operator as a postfix, we have to add it on the right side of the operand, for example:

int num = 5;
print( num++ ); // prints 5
print( num );   // prints 6

In the previous code fragment, the line print( num++) will print five because the original value of num is returned and printed and then increased by one.

Prefix​

When we use the operator as a prefix, we have to add it on the left side of the operand, for example:

int num = 5;
print( ++num ); // prints 6
print( num );   // prints 6

This time, the value of num will be increased by one and then returned. That is why both print will print six.

Example in DartPad​

Let's run some examples in DartPad: