Increment and Decrement Operators

Adding or subtracting 1 from a variable is a very common programming practice.  Adding 1 to a variable is called incrementing and subtracting 1 from a variable is called decrementing.

  • increment and decrement operators work only with integer variables -- not on floating point variables or literals.

  • the C++ compiler is controlling the execution of the prefix and postfix operators.  You cannot change this order of execution.  For example, the parentheses below will not force an early execution: 
    value = (((x--)))* num;   //still decrements x last.

  • one disadvantage of using the increment/decrement operators is that the variable can only be incremented or decremented by the value ONE.  If you need to increment (or decrement) by a larger (or smaller) value, you must use statements like
     m += 2;  or  amount -= 5;

  • be careful when combining increment and decrement operators inside expressions with logical operators.  If in doubt, don't use them together.  For example, do NOT use:
    if (( num1 = = 4 ) || ( num2 != ++j)) 
    (j may not be incremented when (num1 = = 4) is TRUE.)
    Instead, separate the code to avoid this problem:
    if (( num1 = = 4) || (num2 != j))



All are the same:
i = i + 1;
 i += 1;

increment or decrement occurs
before the variable's value is used in the remainder of the expression.

increment or decrement occurs
after the variable's value is used in the remainder of the expression.


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