function of increment/decrement operators and their varieties.

Q2. What is the function of increment/decrement operators? How many varieties do they come in? How are these two varieties different from one another?

Ans. The operator ++ adds 1 to its operand, and – subtracts one. In other words,

a = a + 1;

is the same as:

++a; or a++;

And

a = a- 1;

is the same as

–a; or a–;

However, both the increment and decrement operators come in two varieties: they may either precede or follow the operand. The prefix version comes before the operand (as in ++a or –a) and the postfix version comes after the operand (as in a++ or a–). The two versions have the same effect upon the operand, but they differ when they take place in an expression.

Working with prefix version

When an increment or decrement operator precedes in operand (that is, in its prefix form), C++ performs the increment or decrement operation before using the value of the operand.

For example, the expression

sum = sum + (++count);

will take place in the following fashion. (Assuming the initial values of sum and count are 0 and 10 respectively).

sum                sum        count

  • 0               10                 Initial values
  • 0                11                First increment it

11      =      0       +       11                Now use it

The prefix increment or decrement operators follow change-then-use rule, that is, they first change (increment or decrement) the value of their operand, then use the new value in evaluating the expression.

Working with postfix version

When an increment or decrement operator follows its operand (that is, in its postfix form), C++ first uses the value of the operand in evaluating the expression before incrementing or decrementing the operand’s value.

For example, the expression

sum = sum + count++;

will take place in the following fashion. (Assuming the initial values of sum and count are 0 and 10 respectively).

sum                sum                count

  •             0                       10        Initial values;

10                   0                       10        First use it

10         =        0            +         11        Now increment it

The postfix increment or decrement operators follow use-then-change rule, that is, they first use the value of their operand in evaluating the expression and then change (increment or decrement) the operand’s value.

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