BIM313 – Advanced Programming Techniques

Flow Control

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Contents

• Flow Control– if, switch– while, do-while, for, foreach– Binary operators

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Flow Control

• Branching (if, switch, ternary operator)• Looping (for, while, do-while, foreach)

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Comparison OperatorsOperator Meaning

== equal to

!= not equal to

< less than

> greater than

<= less than or equal to

>= greater than or equal to

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Boolean Variables

• A Boolean variable may take values true or false– bool isWhite = true;– isWhite = false;

• Comparison results can be stored in Boolean variables– bool isLong = (height > 195);– bool isWhite = (color == Color.White);

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Fundamental Logical OperatorsOperator Name Example

&& AND (a > 0) && (a < 10)

|| OR (a <= 0) || (a >= 10)

! NOT !(a < 100)

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The ‘if’ Statement

int height;Console.Write("Enter your height (in cm.) ");height = int.Parse(Console.ReadLine());if (height > 190) Console.WriteLine("You are a tall person!");else Console.WriteLine("Your height is normal!");

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if Statement

if (expression) <statement to execute when expression is true>;

if (expression){ <statement 1>; <statement 2>;}

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if..else

if (expression) <statement to execute when expression is true>;else <statement to execute when expression is false>;

• If there are more statements, use curly brackets.

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Some Notes on ‘if’

• Parentheses are required, they can’t be omitted• Curly braces (‘{’ and ‘}’)should be used if there are

more than one statements:if (test){ statement1; statement2;}

• else part can be omitted• if statements can be nested

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Example: Finding the smallest of 3 integers

int a, b, c, min;Console.WriteLine("Enter 3 integers:");Console.Write("a = ");a = int.Parse(Console.ReadLine());Console.Write("b = ");b = int.Parse(Console.ReadLine());Console.Write("c = ");c = int.Parse(Console.ReadLine());

if (a < b){ if (a < c) min = a; else

min = c;}else{ if (b < c) min = b; else min = c;}

Console.WriteLine("The smallest one is {0}.", min);

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Checking Conditionsif (var1 == 1) { // Do something.}else { if (var1 == 2) { // Do something else. } else { if (var1 == 3 || var1 == 4) { // Do something else. } else { // Do something else. } }

}

if (var1 == 1) { // Do something.}else if (var1 == 2) { // Do something else.}else if (var1 == 3 || var1 == 4) { // Do something else.}else { // Do something else.}

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Common Mistakes

• if (var1 = 1) {…}• if (var1 == 1 || 2) {…}

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The ‘switch’ Statementswitch (<testVar>){ case <comparisonVal1>: <code to execute if <testVar> == <comparisonVal1> > break; case <comparisonVal2>: <code to execute if <testVar> == <comparisonVal2> > break; . . . case <comparisonValN>: <code to execute if <testVar> == <comparisonValN> > break; default: <code to execute if <testVar> != comparisonVals> break;}

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Example 1switch (var1){ case 1: // Do something. break; case 2: // Do something else. break; case 3: case 4: // Do something else. break; default: // Do something else. break;}

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Example 2switch (option){ case 1: Console.WriteLine(“You select 1”); break; case 2: Console.WriteLine(“You select 2”); break; case 3: Console.WriteLine(“You select 3”); break; default: Console.WriteLine(“Please select an integer between 1 and 3.”); break;}

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switch Exampleswitch (strProfession){ case "teacher": MessageBox.Show("You educate our young"); break; case "programmer": MessageBox.Show("You are most likely a geek"); break; case "accountant": MessageBox.Show("You are a bean counter"); break; default: MessageBox.Show("Profession not found in switch statement"); break;}

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In C, only integer values can be used as the expression but in

C#, strings can be used too.

Don’t forget to use breaks!

Example 3switch (strAnimal){ case “bird”: Console.WriteLine(“It has 2 legs.”); break; case “horse”: case “dog”: case “cat”: Console.WriteLine(“It has 4 legs.”); break; case “centipede”: Console.WriteLine(“It has 40 legs.”); break; case “snake”: Console.WriteLine(“It has no legs.”); break; default: Console.WriteLine(“I don’t know that animal!”); break;} 18

The Ternary Operator

• ? :• <test> ? <resultIfTrue> : <resultIfFalse>• Tertiary operator because it acts on 3

operands (remember unary and binary operators acting on 1 and 2 operands resp.)

• Example:– if (a < b) min = a; else min = b;– min = (a < b) ? a : b;

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Looping

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for Loop

for (initializers; check_condition; modifying_expressions){ <statements>}• Example:for (i = 0; i < 10; i++) { Console.WriteLine("i = " + i.ToString());}

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while Loop

while (expression){ <statements>}

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do-while Loop

do{ <statements>} while (expression);

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foreach Loop

foreach (<type> <name> in <list>){ <statements>}

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Displaying Months using for Loop

string[] months = new string[] { "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December" };

for (int i = 0; i < months.Length; i++){ MessageBox.Show(months[i]);}

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Displaying Months using foreach

string[] months = new string[] { "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December" };

foreach (string month in months){ MessageBox.Show(month);}

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Exercise

• Display first ten prime numbers.

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Interrupting Loops

• break – ends the loop immediately• continue – ends the current loop cycle• return – jumps out of the function• goto – jumps to the specified location (don’t use)

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Infinite Loops

while (true){ …}

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Exampleint num;while (true){ Console.Write(“Enter a number between 1 and 100: ”); num = Convert.ToInt32(Console.ReadLine()); if (num >= 1 && num <= 100) break; else { Console.WriteLine(“It should be between 1 and 100.”); Console.WriteLine(“Please try again!\n”); }}

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Bitwise Operators

• & (Bitwise AND)• | (Bitwise OR)• ~ (Bitwise NOT)• ^ (Bitwise XOR)

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Examples

• 0110 & 0101 = 0100 (1&1=1, otherwise 0)• 0110 | 0101 = 0111 (0|0=0, otherwise 1)• 0110 ^ 0101 = 0011 (same0, different1)• ~0110 = 1001 (01, 10)

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Examples

option = Location.Left | Location.Bottom;

if (option & Location.Left != 0) MessageBox.Show(“Indented to left.”);if (option & Location.Bottom != 0) MessageBox.Show(“Indented to right.”);

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Shift Operators

• >> (Shift right)• << (Shift left)• >>=• <<=

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Examples

• int a = 16;• int b = a >> 2; // b becomes 4• int c = a << 4; // c becomes 256• a >>= 2; // a becomes 4• a <<= 4; // a becomes 64

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