C++ Control Structures (Part 2)

Last time we discussed some control structures, today we will discuss switch control structures, assignment and increment decrement operators.

Rvalues and Lvalues:

• Rvalues: these are the expressions that appear on left side of equation, they can be changed (i.e., variables) x = 4;
• Lvalues: these are expressions that appear on right side of equation, they include constants such as numbers (i.e. cannot write 4 = x;)
• Lvalues can be used as Rvalues, but not vice versa.

'Switch' Multiple-Selection Structure:

switch structure tests variable/expression for multiple possible values, a Specific action is to be performed based on the value of an ‘integral expression' (Combination of characters and integers that evaluate to a constant integer value)

Switch statement consists of two parts:

• a controlling expression ie switch (…………)
• and a series of case labels and optional default case, Case labels contain the possible values of the controlling expression
• switch statement compares the value of controlling expression with each case label

flow chart of a switch selection structure (remember, we select one out of many choices) :

the following code example shows the usage of a switch structure:

Output example of this code:

Assignment Operators:

Assignment operators are used for abbreviating assignment expressions

–Addition assignment operator

 c = c + 3;      
c += 3; 

Statements of the form

variable = variable operator expression;

can be rewritten as

variable operator = expression;

Other assignment operators are:

                                   d -= 4     (d = d - 4)

                                   e *= 5     (e = e * 5)

                                   f /= 3     (f = f / 3)

                                   g %= 9     (g = g % 9) 

Increment and Decrement Operator:

Increment operator (++) - can be used instead of

         c += 1 OR c = c + 1

Decrement operator (--) - can be used instead of

         c -= 1 OR c = c - 1

Preincrement:

         Whenever the operator is used before the variable (++c or ––c) then first the variable is changed, then the expression it is in is evaluated.

Postincrement:

         Whenever the operator is used after the variable (c++ or c--), the the expression the variable is in executes, then the variable is changed

for example, If c = 5, then

         cout << ++c;

       c is changed to 6, then printed out

      cout << c++;

       Prints out 5 (cout is executed before the increment, c then becomes 6)

When variables are not in expression:

then preincrementing and postincrementing have same effect

++c;

cout << c;

and 

c++;

cout << c;

are the same