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CMSC 150 conditional execution

CMSC 150 conditional execution. CS 150: Mon 16 Jan 2012. Sequential Execution. import java.util.Scanner ; public class ProgramFive { public static void main(String [] args ) { Scanner keyboard = new Scanner( System.in ); System.out.println ( “Enter sphere radius:“ );

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CMSC 150 conditional execution

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  1. CMSC 150conditionalexecution CS 150: Mon 16 Jan 2012

  2. Sequential Execution import java.util.Scanner; public class ProgramFive { public static void main(String[] args) { Scanner keyboard = new Scanner( System.in ); System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble(); double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius; System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume ); } } Java executes statements step-by-step in exactly the order you have them

  3. Sequential Execution import java.util.Scanner; public class ProgramFive { public static voidmain(String[] args) { Scanner keyboard = new Scanner( System.in ); System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble(); double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius; System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume ); } }

  4. Sequential Execution import java.util.Scanner; public class ProgramFive { public static void main(String[] args) { Scanner keyboard = new Scanner( System.in ); System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble(); double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius; System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume ); } }

  5. Sequential Execution import java.util.Scanner; public class ProgramFive { public static void main(String[] args) { Scanner keyboard = new Scanner( System.in ); System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble(); double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius; System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume ); } }

  6. Sequential Execution import java.util.Scanner; public class ProgramFive { public static void main(String[] args) { Scanner keyboard = new Scanner( System.in ); System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble(); double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius; System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume ); } }

  7. Sequential Execution import java.util.Scanner; public class ProgramFive { public static void main(String[] args) { Scanner keyboard = new Scanner( System.in ); System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble(); double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius; System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume ); } }

  8. Sequential Execution import java.util.Scanner; public class ProgramFive { public static void main(String[] args) { Scanner keyboard = new Scanner( System.in ); System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble(); double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius; System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume ); } }

  9. Sequential Execution import java.util.Scanner; public class ProgramFive { public static void main(String[] args) { Scanner keyboard = new Scanner( System.in ); System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble(); double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius; System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume ); } }

  10. Sequential Execution import java.util.Scanner; public class ProgramFive { public static void main(String[] args) { Scanner keyboard = new Scanner( System.in ); System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble(); double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius; System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume ); } }

  11. How Is This Different? import java.util.Scanner; public class ProgramFive { public static void main(String[] args) { Scanner keyboard = new Scanner( System.in ); double radius = keyboard.nextDouble(); double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius; System.out.println( “Enter sphere radius:“ ); System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume ); } }

  12. How Is This Different? import java.util.Scanner; public class ProgramFive { public static void main(String[] args) { Scanner keyboard = new Scanner( System.in ); double radius = keyboard.nextDouble(); double pi = 3.14159; double volume = (4.0 / 3.0) * pi * radius * radius * radius; System.out.println( “Enter sphere radius:“ ); System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume ); } }

  13. Now, How Is This Different? import java.util.Scanner; public class ProgramFive { public static void main(String[] args) { Scanner keyboard = new Scanner( System.in ); System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble(); double volume = (4.0 / 3.0) * pi * radius * radius * radius; double pi = 3.14159; System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume ); } }

  14. Now, How Is This Different? import java.util.Scanner; public class ProgramFive { public static void main(String[] args) { Scanner keyboard = new Scanner( System.in ); System.out.println( “Enter sphere radius:“ ); double radius = keyboard.nextDouble(); double volume = (4.0 / 3.0) * pi * radius * radius * radius; double pi = 3.14159; System.out.println( “The volume of a sphere with radius “ + radius + “ is “ + volume ); } } Will not compile! Trying to use a variable before it is declared

  15. Find the Runtime Error import java.util.Scanner; public class ExampleProgram { public static void main(String[] args) { Scanner keyboard = new Scanner( System.in ); System.out.println( “Enter an integer:” ); intfirstNumber = keyboard.nextInt(); System.out.println( “Enter another integer:” ); intsecondNumber = keyboard.nextInt(); double ratio = (double) firstNumber / secondNumber; System.out.println( “The ratio is “ + ratio ); } }

  16. Find the Runtime Error import java.util.Scanner; public class ExampleProgram { public static void main(String[] args) { Scanner keyboard = new Scanner( System.in ); System.out.println( “Enter an integer:” ); intfirstNumber = keyboard.nextInt(); System.out.println( “Enter another integer:” ); intsecondNumber = keyboard.nextInt(); double ratio = (double) firstNumber / secondNumber; System.out.println( “The ratio is “ + ratio ); } } potentially…

  17. Conditional Execution // lots of your great code … if ( condition ) { statement; } … // lots more of your great code Java will execute the statement only if the condition is true

  18. Conditional Execution // lots of your great code … double ratio = 0.0; if ( secondNumber != 0 ) { ratio = (double) firstNumber / secondNumber; } … // lots more of your great code a Boolean condition

  19. Conditional Execution // lots of your great code … double ratio = 0.0; if ( secondNumber != 0 ) { ratio = (double) firstNumber / secondNumber; } … // lots more of your great code Java will compute the ratio only if the condition is true (i.e., non-zero second #)

  20. Note The Difference… // lots of your great code … double ratio = 0.0; if ( secondNumber != 0 ) { ratio = (double) firstNumber / secondNumber; } … // lots more of your great code // lots of your great code … if ( secondNumber != 0 ) { double ratio = (double) firstNumber / secondNumber; } … // lots more of your great code

  21. Note The Difference… // lots of your great code … double ratio = 0.0; if ( secondNumber != 0 ) { ratio = (double) firstNumber / secondNumber; } … // lots more of your great code // lots of your great code … if ( secondNumber != 0 ) { double ratio = (double) firstNumber / secondNumber; } … // lots more of your great code the variable ratio will not be accessible outside the if statement!

  22. Conditions • Boolean expressions • Must evaluate to true or false • Comparison operators: • ==, <, >, <=, >=, != • Compound expressions: • Logical and: && • Logical or: || • Logical not: !

  23. Truth Tables P, Q can be any Boolean expression (perhaps compound)

  24. Compound Expressions • firstNumber == 0 && secondNumber == 0 • firstNumber < 0 && secondNumber < 0 • firstNumber > 0 && !(secondNumber > 0) • firstNumber == 0 || secondNumber == 0 • firstNumber < 0 && firstNumber > 0 • firstNumber < 0 || firstNumber > 0 • !( firstNumber == 0 || secondNumber == 0 )

  25. If / If-Else / If-Else-If • if ( condition ) { statement; } • if ( condition ) { statement; } else { statement; } • if ( condition ) { statement; } else if ( condition ) { statement; } else { statement; }

  26. Understanding Conditionals if ( secondNum != 0 ) { ratio = firstNum / secondNum; } if ( secondNum == 0 ) { System.out.println( “Divide by zero!” ); } if ( secondNum != 0 ) { ratio = firstNum / secondNum; } else { System.out.println( “Divide by zero!” ); }

  27. Understanding Conditionals String sign; if ( number == 0 ) { sign = “non-negative”; } else if ( number < 0 ) { sign = “negative”; } else if ( number > 0 ) { sign = “positive”; } String sign; if ( number == 0 ) { sign = “non-negative”; } if ( number < 0 ) { sign = “negative”; } if ( number > 0 ) { sign = “positive”; }

  28. Understanding Conditionals String sign; if ( number == 0 ) { sign = “non-negative”; } else if ( number < 0 ) { sign = “negative”; } else { sign = “positive”; } String sign; if ( number == 0 ) { sign = “non-negative”; } if ( number < 0 ) { sign = “negative”; } else { sign = “positive”; }

  29. Understanding Conditionals String sign; if ( number == 0 ) { sign = “non-negative”; } else if ( number < 0 ) { sign = “negative”; } else { sign = “positive”; } String sign; if ( number == 0 ) { sign = “non-negative”; } if ( number < 0 ) { sign = “negative”; } else { sign = “positive”; }

  30. Understanding Conditionals String sign; if ( number == 0 ) { sign = “non-negative”; } else if ( number < 0 ) { sign = “negative”; } else { sign = “positive”; } String sign; if ( number == 0 ) { sign = “non-negative”; } if ( number < 0 ) { sign = “negative”; } if ( number > 0 ) { sign = “positive”; }

  31. Compound Statements • if ( condition ) { statement; statement; statement; … } • if ( condition ) { statement; statement; statement; … } else { statement; statement; statement; … } To Java, this is a single statement

  32. Compound Statements • if ( condition ) { statement; statement; statement; … } • if ( condition ) { statement; statement; statement; … } else { statement; statement; statement; … } Statements inside can be anything… Even another if statement!

  33. Nested Conditionals • if ( condition_1 ) { if ( condition_2 ) { statement_1; } else { statement_2; } }

  34. Nested Conditionals • if ( condition_1 && condition_2 ) { statement_1; } if ( !condition_2 ) { statement_2; } • if ( condition_1 ) { if ( condition_2 ) { statement_1; } else { statement_2; } }

  35. Nested Conditionals • if ( condition_1 && condition_2 ) { statement_1; } if ( !condition_2 ) { statement_2; } • if ( condition_1 ) { if ( condition_2 ) { statement_1; } else { statement_2; } }

  36. Nested Conditionals • if ( condition_1 && condition_2 ) { statement_1; } if ( condition_1 && !condition_2 ) { statement_2; } • if ( condition_1 ) { if ( condition_2 ) { statement_1; } else { statement_2; } }

  37. Changing The Flow ... System.out.println( “Enter another integer:” ); intsecondNumber = keyboard.nextInt(); if ( secondNumber != 0 ) { double ratio = (double) firstNumber / secondNumber; System.out.println( “The ratio is “ + ratio ); } else { System.out.println( “Divide by zero error!” ); } ... 21 firstNumber 7 secondNumber

  38. Changing The Flow ... System.out.println( “Enter another integer:” ); intsecondNumber = keyboard.nextInt(); if ( secondNumber != 0 ) { double ratio = (double) firstNumber / secondNumber; System.out.println( “The ratio is “ + ratio ); } else { System.out.println( “Divide by zero error!” ); } ... 21 firstNumber 7 secondNumber

  39. Changing The Flow ... System.out.println( “Enter another integer:” ); intsecondNumber = keyboard.nextInt(); if ( secondNumber != 0 ) { double ratio = (double) firstNumber / secondNumber; System.out.println( “The ratio is “ + ratio ); } else { System.out.println( “Divide by zero error!” ); } ... 21 firstNumber 7 secondNumber 3 ratio

  40. Changing The Flow ... System.out.println( “Enter another integer:” ); intsecondNumber = keyboard.nextInt(); if ( secondNumber != 0 ) { double ratio = (double) firstNumber / secondNumber; System.out.println( “The ratio is “ + ratio ); } else { System.out.println( “Divide by zero error!” ); } ... 21 firstNumber 7 secondNumber 3 ratio

  41. Changing The Flow ... System.out.println( “Enter another integer:” ); intsecondNumber = keyboard.nextInt(); if ( secondNumber != 0 ) { double ratio = (double) firstNumber / secondNumber; System.out.println( “The ratio is “ + ratio ); } else { System.out.println( “Divide by zero error!” ); } ... 21 firstNumber 0 secondNumber

  42. Changing The Flow ... System.out.println( “Enter another integer:” ); intsecondNumber = keyboard.nextInt(); if ( secondNumber != 0 ) { double ratio = (double) firstNumber / secondNumber; System.out.println( “The ratio is “ + ratio ); } else { System.out.println( “Divide by zero error!” ); } ... 21 firstNumber 0 secondNumber

  43. Changing The Flow ... System.out.println( “Enter another integer:” ); intsecondNumber = keyboard.nextInt(); if ( secondNumber != 0 ) { double ratio = (double) firstNumber / secondNumber; System.out.println( “The ratio is “ + ratio ); } else { System.out.println( “Divide by zero error!” ); } ... 21 firstNumber 0 secondNumber

  44. Let’s Hunt The Wumpus

  45. Our Maze PIT

  46. Our Rules • Player can move one step per turn • up, down, left, or right • cannot move off the maze (grid) • Find the gold  win • Find the wumpus  lose • Find the pit  lose a turn • Player gets only four turns, otherwise draw PIT

  47. Location In The Maze 0 2 1 0 PIT 1 2

  48. Handle Player Movement First… 0 2 1 0 1 2

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