CSci 125 Lecture 10 Martin van Bommel

Simple Statements Expression followed by semicolon Assignments total = n1 + n2; Function calls printf(”Hello.\n”); Useless statements n1 + n2;

Embedded Assignments Assignment expression can be used as part of a larger expression in a statement Its value is the value assigned z = (x = 6) + y; x is assigned value 6, then z assigned 6 + y Difficult to read Used rarely and only when makes sense

Multiple Assignments Embedded assignments useful to set several variables to the same value n1 = n2 = n3 = 0; Assignment operator evaluated right to left Avoid mixed types; e.g. double d and int i d = i = 1.5; Assigns i value 1, thus 1 assigned to d

Statement Blocks Sequence of statements that specify a coherent unit enclosed in curly braces E.g. if, for, while statement bodies { statement 1 statement 2... }

Boolean Data Conditionals test expressions whose values are either TRUE or FALSE George Boole - developed algebra for T/F Standard C has no Boolean type We use the integer 0 for FALSE and the integer 1 for TRUE

Relational Operators Compare two atomic values (not strings) Precedence after +/- > Greater than < Less than >= Greater or equal <= Less or equal Next level of precedence == Equal != Not equal

Logical Operators Operate on other Boolean values (in order of precedence) !Not ( TRUE if operand FALSE ) && And ( TRUE if both TRUE ) || Or ( TRUE if either TRUE )

Example 1 “ x is not equal to either 2 or 3” if (x != 2 || x != 3) No, it should be if (!(x == 2 || x == 3)) or if (x != 2 && x != 3)

Example 2 “x is in the range from 0 to 10 exclusive” if (0 < x < 10) No, it should be if (0 < x && x < 10)

Short-Circuit Evaluation Evaluating exp1 && exp2 or exp1 || exp2 evaluates expressions from left to right If answer known before both evaluated, second expression not evaluated (x != 0) && (y % x == 0)

Flags Variables used for testing truth values int done; Assign value to indicate state of flag done = 0; or done = 1;

Setting Flags To set a flag on a condition, could use if (input == -1) { done = 1; } else { done = 0; } Better to simply use done = (input == -1);

Testing a Flag To test whether done has value TRUE, could use if (done == 1) Better to simply use if (done) Test for truth value 1 is redundant

Boolean Example Leap year every fourth year, except centuries, then just every fourth century –year is divisible by 4 but not by 100, or –year is divisible by 400 Try ((y % 4 == 0) && (y % 100 != 0)) || (y % 400 == 0)