Expression Review what is the result and type of these expressions? int x=2, y=15; double u=2.0, v=15.0; -x x+y x-y x*v y / x x/y y%x x%y u*v u/v v/u u%v x * u (x+y)*u u /(x-x) x++; u++; u = --x; u = x--; u *= ++x; v /= x;

Constants and Variables Review are these constants legal? .5 5.E 0.5e3 0.5E-3 0.5E-3.5 ’a’ ’%’ ’Ab’ ”Ab” are these variable names legal? MyTotal My_Total __MyTotal My Total what does this mean? int mytotal=0; int yourtotal(1); what would be stored in myvar? int myvar; myvar=2.56; is this code correct? const int i=55; ++i; what would be stored in yourvar? double yourvar; yourvar=5/2;

Logical Expressions, IF

Boolean Algebra Boolean (logical) expressions can have two values true or false branch of mathematics that deals with this type of logic is called Boolean algebra developed by British mathematician George Boole in the 19th century logical operators in C++ && - logical “and”, binary || - logical “or”, binary ! - logical “not”, unary

Truth Table for && truth table - lists all combinations of operand values and the result of the operator for each combination truth table for && (logical “and’) p q p && q false false false false true false true false false true true true

Truth Tables for II and ! p !p false false false false true p q p || q false false false false true true true false true true true true p !p false true true false

Boolean Algebra ! (p && q) p q p && q !(p && q) false false false true can create complex logical expressions by combining with subexpressions example ! (p && q) a truth table can be used to determine when a logical expression is true note that & and | are also legal operators, make sure to use correct ones p q p && q !(p && q) false false false true false true false true true false false true true true true false

Example Logical Expressions bool p = true; bool q = false; bool r = true; bool s = p && q; bool t = p && !q bool u = !q || r; bool v = p || !q || !r; bool w = p && q && !r; bool x = q || (p && r); bool y = !(r && !q); bool z = !(p && q && r);

Relational Operators equality operators == note the two equal signs != examples int i = 32; int k = 45; bool q = i == k; bool r = i != k;

Relational Operators ordering operators < > >= () <= () >= () <= () examples int i = 5; int k = 12; bool p = i < 10; bool q = k > i; bool r = i >= k; bool s = k <= 12;

Operator Precedence Expanded precedence of operators (from highest to lowest) () Unary + - * / % + - > < >= <= != == && || =

Examples of Logical Expressions int a = 5, b = 10, c = 20; bool d = a < b; bool e = a > b; bool f = (a > b) || (b < c ); bool g = (a > b) && (b < c ); bool h = !(a < b); bool i = !(a==b); bool j = 2*a == b; bool k = (a+b) >= c; bool l = !((a+b) != c); bool m = (a+b) == (c-a); bool n = (a+b) >= (c-a); int o=a; int p=o=b; // what is the outcome of this statement? bool q=true; q = d = false;

Operator Precedence Revisited same or different? (a*b)+c a*b + c a*(b+c) a*b + c (a+b) > c a + b > c a+(b>c) a + b > c (a > b) == (b > c) a > b == b > c (a == b) > (b == c) a == b > b == c (a != b) && (c <= d) a != b && c <= d (a > b) && (c || d) a > b && c || d (a = b) && c a = b && c

Conditional Constructs provide ability to control whether a statement is executed constructs if-statement if if-else if-else-if switch-statement conditional statement

Blocks and Local Variables a list of statements enclosed in curly brackets is called a block block may be placed anywhere a statement can be placed (note the placement of brackets: if ((saleType == ’W’) || (saleType == ’w’)) { total = price * number; } a variable can be declared and used within block, such variable is local to the block and does not exist outside of it else if ((saleType == ’R’) || (saleType == ’r’)){ double subtotal; subtotal = price * number; total = subtotal + subtotal * taxRate; variable scope – area in program where a variable can be used what’s the scope of a variable local block? accessing variable outside the block is an error

The Basic If-Statement syntax if (expression) body if the expression is true then execute action body is either a single statement or a block example 1: if (v > 0) v = 0; example 2: if (v < 0) { v = -v; ++i; } expression body true false

Sorting Two Numbers cout << "Enter two integers: "; int n1, n2; cin >> n1 >> n2; if (n1 > n2) { const int tmp = n1; n1 = n2; n2 = tmp; } cout << ”Numbers in order: “ << n1 << " " << n2 << endl; programming idiom – a common way of accomplishing a simple task swapping values of two variables with a third is an idiom

The If-Else Statement expression false true body1 body2 syntax if (expression) body1 else body2 if expression is true then execute body1 otherwise execute body2 if (v == 0) cout << "v is 0"; else cout << "v is not 0"; expression false true body1 body2

Nested Ifs nested if - one if is the body or inside the block of another outer if – enclosing if inner If – enclosed if if (n1 > n2) // outer if if (n2 > n3) // inner if is the body of outer if cout << n3; // no need for curly brackets if (n1 > n2) { // outer if i++; if (n2 > n3) // inner if inside block of outer if cout << n3; } nesting may be more than two if-s deep

Selection want to carry out actions depending on the value of an expression two major ways to do this multiway if-statement if-else statements “glued” together switch statement

Multiway If-Statement example int vclass; cout << "Enter the vehicle class: "; cin >> vclass; if (vclass == 1) cout << ”Passenger car”; else if (vclass == 2) cout << ”Bus”; else if (vclass == 3) cout << ”Truck”; else cout << ch << ”Unknown vehicle class!”;

Switch Statement syntax switch (expression){ case constant: statements break; default: statements } semantics expression is evaluated, execution continues in first matching case (optional) default matches any expression value break-statement terminates the switch statement, execution continues with a statement following switch-block if case does not end with break, execution continues to next case expression of any “countable” type (int, char) literal or named constant of same type as expression

Switch Example 1 int vclass; cout << "Enter the vehicle class: "; cin >> vclass; switch (vclass){ case 1: cout << "Passenger car"; break; case 2: cout << "Bus"; default: cout << "Unknown vehicle class! "; break; // unnecessary but used for consistency }

Switch Example 2 cout << "Enter simple expression: "; int Left; int Right; char Operator; cin >> Left >> Operator >> Right; cout << Left << " " << Operator << " " << Right << " = "; switch (Operator) { case '+' : cout << Left + Right << endl; break; case '-' : cout << Left - Right << endl; break; case '*' : cout << Left * Right << endl; break; case '/' : cout << Left / Right << endl; break; default: cout << "Illegal operation" << endl; }

Arity and Conditional Operator ternary operator – operator accepting three operands conditional operator is used as an abbreviated form of branching boolean-expression ? true-expression : false-expression if boolean-expression is true, then the value of whole expression is true-expression, or false-expression otherwise conditional assignment statement – conditional operator is used to assign value to variable what branching construct is this assignment statement equivalent to? int i = j>0 ? j : -j; program that calculates the larger number (of two) int main() { int n1, n2; cin >> n1 >> n2; int max = n1 > n2 ? n1 : n2; cout << ”maximum is ” << max << endl; } arity (again) – number of operands an operator accepts. What arities have we studied?

Debugging and Tracing Programs specially compiled executables leave information the original source file: names of variables and source lines this allows program tracing – suspending program execution at specific source line and executing program one source line at a time variable watching – observing values stored in source program variables breakpoint – line in the source program where execution has to be suspended