Conditions, Logical Expressions, and Selection Control Structures ROBERT REAVES

Flow of Control  The order in which the computer executes statements in a program.  Normally sequential.  How to make it not sequential, we use control structures.  It is a statement used to alter the normally sequential flow of control.

Selection  Used when we want the computer to choose between alternative actions. Assertion Statement 1BStatement 1A false true

Bool Data Type  Built-in type consists of just TWO values, the constants true and false.  bool is short for boolean.  Used for testing conditions in a program so the computer can make a decision.  Ex:  bool dataOK;  bool done;  bool taxable;  True and false are not variable names and they aren’t strings. They are special constants in C++, and are reserved words.

Logical Expressions  These assertions are also called boolean expressions.  Assigning a Boolean variable:  done = true; // This is valid because we are assuming it is pre-declared.  Another way, with a relational operator:  lessThan = (5 < 3); // What do you think is in the variable lessThan?

Relational Operator  ==Equal to  !=Not equal to  >Greater than  <Less than  >=Greater than or equal to  <=Less than or equal to  An expressions follow by a relational operator followed by an expression is called a relational expression.

Relational Operator  Compare like types to avoid conflicts.  What do you think true and false represent in numerical form?  VERY VERY VERY VERY VERY VERY VERY VERY VERY IMPORTANT  (=) and (==) are COMPLETELY different.  (=) assigns a value to some variable.  (==) compares two variables. (equals-equals)

Comparing Strings  myStr < yourStr // string object and string object, OKAY  myStr >= “Johnson” // string object and c string, OKAY  “NO” <= “STOP NOW” // cannot both be C strings, NOOOOOO  String comparisons begin with the first character of each string.  Continues to compare a character at a time, until a mismatch is found or the final characters have been compared and are equal.  Character values based on ASCII chart.

If-then & if-then-else statement  if(expression)  statement1A  else  statement1B  Notice there are no (;) after the else or if!  Only used on simple statements such as assignment statements, input statements, and output statements.