Conditions, Logical Expressions, and Selection Control Structures

1. Conditions, Logical Expressions, and Selection Control Structures Robert reaves

2. 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.

3. Selection • Used when we want the computer to choose between alternative actions. Assertion false true Statement 1A Statement 1B

4. Bool Data Type • Built-in type consists of just TWO values, the constants true and false. • boolis short for boolean. • Used for testing conditions in a program so the computer can make a decision. • Ex: • booldataOK; • 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.

5. 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?

6. 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.

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

8. 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.

9. 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.