Expressions, Conditionals and

Looping

Expressions, Conditionals and

Looping

CS 3260Version 1.0

CS 3260Version 1.0

OverviewOverview

• Statements• Expressions• Operators• Selection (Conditionals)• Iteration (Loop)

• Statements• Expressions• Operators• Selection (Conditionals)• Iteration (Loop)

C# Statement TypesC# Statement Types

Category C# keywords

Selection statements if, else, switch, case

Iteration statements do, for, foreach, in, while

Jump statements break, continue, default, goto, return, yield

Exception handling statements throw, try-catch, try-finally, try-catch-finally

checked and unchecked checked, unchecked

fixed statement fixed

lock statement lock

StatementsStatements• Declaration

– Variable– Method

• Blocks { … }• Expression• Selection (Conditional)

– if/if-else/switch/?:

• Iteration (Loop)– while/do-while/for/foreach

• Declaration– Variable– Method

• Blocks { … }• Expression• Selection (Conditional)

– if/if-else/switch/?:

• Iteration (Loop)– while/do-while/for/foreach

StatementsStatements• Statement Lists { … }• ; - Empty• <label>: <statement>;• Declaration - <type> <ident> = <init>;• Expression• Selection (Conditional)• Iteration (Loop)

• Statement Lists { … }• ; - Empty• <label>: <statement>;• Declaration - <type> <ident> = <init>;• Expression• Selection (Conditional)• Iteration (Loop)

Jump StatementsJump Statements

• goto <label> - jump to label• break – switch/loops• continue - loops• return – no-value/value• throw – Exception object• yield – continue/break

• goto <label> - jump to label• break – switch/loops• continue - loops• return – no-value/value• throw – Exception object• yield – continue/break

Exception Handling Statementschecked/unchecked Block

Exception Handling Statementschecked/unchecked Block

• try-catch-finally• checked/unchecked

• try-catch-finally• checked/unchecked

try-catch-finallytry-catch-finally

• try: try-blockcatch(...) { //catch-block-1 }...catch(...) { //catch-block-n }

• try: try-block finally: finally-block

• try: try-blockcatch(...) { //catch-block-1 }...catch(...) { //catch-block-n }

• try: try-block finally: finally-block

using Statementsusing Statements

• using <namespace>• using ( resource-acquisition )

embedded-statement

• using <namespace>• using ( resource-acquisition )

embedded-statement

Other StatementsOther Statements

• lock • yield• fixed

• lock • yield• fixed

lock Statementlock Statement

• lock ( expr ) embedded-statement• lock ( expr ) embedded-statement

yield Statementyield Statement

• yield return expr ;• yield break;

• yield return expr ;• yield break;

Statement ExampleLocal variable declaration static void () {

int a; int b = 2, c = 3; a = 1;Console.WriteLine(a + b + c);

}Local constant declaration static void () {

const float pi = 3.1415927f;const int r = 25;Console.WriteLine(pi * r * r);

}Expression statement static void () {

int i;i = 123;// Expression statementConsole.WriteLine(i); // Expression statementi++; // Expression statementConsole.WriteLine(i); // Expression statement

}if statement static void (string[] args) {

if (args.Length == 0) {Console.WriteLine("No arguments");

}else {

Console.WriteLine("One or more arguments");}

}

switch statement static void (string[] args) {int n = args.Length;switch (n) {

case 0:Console.WriteLine("No arguments");break;

case 1:Console.WriteLine("One argument");break;

default:Console.WriteLine("{0} arguments", n);break;

}}

while statement static void (string[] args) {int i = 0;while (i < args.Length) {

Console.WriteLine(args[i]);i++;

}}

do statement static void () {string s;do {

s = Console.ReadLine();if (s != null) Console.WriteLine(s);

} while (s != null);}

for statement static void (string[] args) {for (int i = 0; i < args.Length; i++) {

Console.WriteLine(args[i]);}

}foreach statement static void (string[] args) {

foreach (string s in args) {Console.WriteLine(s);

}}

break statement

static void () {while (true) {

string s = Console.ReadLine();if (s == null) break;Console.WriteLine(s);

}}

continue statement

static void (string[] args) {for (int i = 0; i < args.Length; i++) {

if (args[i].StartsWith("/")) continue;Console.WriteLine(args[i]);

}}

goto statement static void (string[] args) {int i = 0;goto check;loop:Console.WriteLine(args[i++]);check:if (i < args.Length) goto loop;

}return statement static int Add(int a, int b) {

return a + b;}

static void () {Console.WriteLine(Add(1, 2));return;

}yield statement static IEnumerable<int> Range(int from, int to) {

for (int i = from; i < to; i++) {yield return i;

}yield break;

}

static void Main() {foreach (int x in Range(-10,10)) {

Console.WriteLine(x);}

}

throw and trystatements

static double Divide(double x, double y) {if (y == 0) throw new DivideByZeroException();return x / y;

}

static void (string[] args) {try {

if (args.Length != 2) {throw new Exception("Two numbers

required");}double x = double.Parse(args[0]);double y = double.Parse(args[1]);Console.WriteLine(Divide(x, y));

}catch (Exception e) {

Console.WriteLine(e.Message);}finally {

Console.WriteLine(“Good bye!”);}

}

checked and unchecked statements

static void () {int i = int.MaxValue;checked {Console.WriteLine(i + 1); // Exception}unchecked {Console.WriteLine(i + 1); // Overflow}

}

lock statement class Account{

decimal balance;

public void Withdraw(decimal amount) { lock (this) { if (amount > balance) {

throw new Exception("Insufficient funds"); } balance -= amount; }}

}using statement static void () {

using (TextWriter w = File.CreateText("test.txt")) {w.WriteLine("Line one");w.WriteLine("Line two");w.WriteLine("Line three");

}}

ExpressionsExpressions

• Primary• void• Arithmetic• Assignment

• Primary• void• Arithmetic• Assignment

OperatorsOperators

• Operators• Precedence• Associativy

• Operators• Precedence• Associativy

C# operators (categories in order of precedence)

Category Operator symbol Operator name Example User-overloadablePrimary ( ) Grouping while(x) No  . Member access x.y No  -> Pointer to struct (unsafe) x->y No  ( ) Function call x( ) No  [] Array/index a[x] Via indexer  ++ Post-increment x++ Yes  -- Post-decrement x-- Yes  new Create instance new Foo( ) No  stackalloc Unsafe stack allocation stackalloc(10) No  typeof Get type from identifier typeof(int) No  checked Integral overflow check on checked(x) No  unchecked Integral overflow check off unchecked(x) NoUnary sizeof Get size of struct sizeof(int) No  + Positive value of +x Yes  - Negative value of -x Yes  ! Not !x Yes  ~ Bitwise complement ~x Yes  ++ Pre-increment ++x Yes  -- Post-decrement --x Yes  ( ) Cast (int)x No  * Value at address (unsafe) *x No  & Address of value (unsafe) &x NoMultiplicative * Multiply x * y Yes  / Divide x / y Yes  % Remainder x % y YesAdditive + Add x + y Yes  - Subtract x - y Yes

Shift << Shift left x >> 1 Yes  >> Shift right x << 1 YesRelational < Less than x < y Yes  > Greater than x > y Yes  <= Less than or equal to x <= y Yes  >= Greater than or equal to x >= y Yes  is Type is or is subclass of x is y No  as Type conversion x as y NoEquality == Equals x == y Yes  != Not equals x != y YesLogical And & And x & y YesLogical Xor ^ Exclusive Or x ^ y YesLogical Or | Or x | y YesConditional And && Conditional And x && y Via &Conditional Or || Conditional Or x || y Via |

Null Coalescing

?? Null Coalescing x ?? y No

Conditional ?: Conditional isTrue ? thenThisValue : elseThisValue NoAssignment = Assign x = y No  *= Multiply self by x *= 2 Via *  /= Divide self by x /= 2 Via /  += Add to self x += 2 Via +  -= Subtract from self x -= 2 Via -  <<= Shift self left by x <<= 2 Via <<  >>= Shift self right by x >>= 2 Via >>  &= And self by x &= 2 Via &  ^= Exclusive-Or self by x ^= 2 Via ^  |= Or self by x |= 2 Via |Lambda => Lambda x => x + 1 No

SuffixesSuffixes

real-type-suffix: one ofF f D d M m

Selection - ConditionalSelection - Conditional• if (<boolean expression>) <statement>;• if(<boolean expression>) <statement>

else <statement>;• switch(<integer expression)

{ <statements> }• <datatype> <ident> = (<expression)?

<true_value>:<false_value>

• if (<boolean expression>) <statement>;• if(<boolean expression>) <statement>

else <statement>;• switch(<integer expression)

{ <statements> }• <datatype> <ident> = (<expression)?

<true_value>:<false_value>

if - Selectionif - Selection

• if ( expr ) then-stmt else else-stmt• if ( expr ) then-stmt else else-stmt

Iteration - LoopIteration - Loop• while(<bool expression>) <statement>;• do <statement> while(<bool expression);• for(<init statement>; <bool expr>; <change

statement>;) <statement>;• foreach(<type> <ident> <type> in <ident>)

<statement>;

• while(<bool expression>) <statement>;• do <statement> while(<bool expression);• for(<init statement>; <bool expr>; <change

statement>;) <statement>;• foreach(<type> <ident> <type> in <ident>)

<statement>;

while - Loopwhile - Loop

• while-statement:while ( boolean-expression )

embedded-statement

• while-statement:while ( boolean-expression )

embedded-statement

do loopdo loop

• do-body while ( expr ) ;• do-body while ( expr ) ;

for - Loopfor - Loop

• for ( for-initializer ; for-condition ; for-iterator ) embedded-statement

• for ( for-initializer ; for-condition ; for-iterator ) embedded-statement

foreach Loopforeach Loop

• foreach(<datatype> <ident> in <enumerable_collection>)

• <statement(s)>

• foreach(<datatype> <ident> in <enumerable_collection>)

• <statement(s)>

throw - returnthrow - return

• throw expr ;• return expr ; or return ;

• throw expr ;• return expr ; or return ;

Executable StatementsExecutable Statements• Methods• Properties• Events• Indexers• User-defined operators• Instance constructors• Static constructors• Destructors

• Methods• Properties• Events• Indexers• User-defined operators• Instance constructors• Static constructors• Destructors