4B. Abbreviations for Assignments

Abbreviations for assignments

Increment and decrement

It is common to find that you want to change a variable by adding or subtracting 1. Of course,

  n = n + 1;

will change n to have a value one larger than its former value. But there are some convenient abbreviations. Statement

  n++;

means the same thing as n = n + 1; and statement

  n--;

is equivalent to statement n = n - 1;

Operator assignment

Statement

  x += E;

is equivalent to

  x = x + (E);

For example,

  kangaroo += 2;

is equivalent to

  kangaroo = kangaroo + 2;

You can use any binary operator (+, -, *, etc.) with =. For example, statement

  x *= n + 1;

has the same effect as statement

  x = x * (n+1);

Do not use ++ or -- in expressions

It is common for students to confuse x++ with x+1. But the two have very different meanings: x++ changes the value of variable x, but x+1 does not change x.

The coding standards for this course require that you only use abbreviations such as x++ and x-- as statements, not as expressions. Never write x++ as a parameter of a function.

Summary

Abbreviations for assignment statements include x++, which abbreviates x = x + 1, and x--, which abbreviates x = x - 1.

Exercises

What does
```
  robinHood++;
```
abbreviate? Answer
What does
```
  lazy *= w + 1;
```
abbreviate? Answer
Does
```
  int x = 0;
  x = x++;
```
make sense? If so, what is the value of x after doing both lines? Answer

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