C++ problem solving operators ( conditional operators,logical operators, switch statements)
- 1. ا ِ ن ٰم ْ حَّ الر ِهللا ِ م ْ سِب ِ مْي ِ حَّ لر 1
- 4. Relational Operators • Used to compare numbers to determine relative order • Operators: > Greater than < Less than >= Greater than or equal to <= Less than or equal to == Equal to != Not equal to 4
- 5. Relational Expressions • Boolean expressions – true or false • Examples: 12 > 5 is true 7 <= 5 is false if x is 10, then x == 10 is true, x != 8 is true, and x == 8 is false 5
- 6. Relational Expressions • Can be assigned to a variable: result = x <= y; • Assigns 0 for false, 1 for true • Do not confuse = and == 6
- 8. The if Statement • Allows statements to be conditionally executed or skipped over • Models the way we mentally evaluate situations: – "If it is raining, take an umbrella." – "If it is cold outside, wear a coat." 8
- 9. Flowchart for Evaluating a Decision 9
- 10. The if Statement • General Format: if (expression) statement; 10
- 11. The if Statement-What Happens To evaluate: if (expression) statement; • If the expression is true, then statement is executed. • If the expression is false, then statement is skipped. 11
- 12. if Statement in Program 4-2 Continued… 12
- 13. if Statement in Program 4-2 13
- 14. Flowchart for Program 4-2 Lines 21 and 22 14
- 15. if Statement Notes • Do not place ; after (expression) • Place statement; on a separate line after (expression), indented: if (score > 90) grade = 'A'; • Be careful testing floats and doubles for equality • 0 is false; any other value is true 15
- 16. 4.3 Expanding the if Statement 16
- 17. Expanding the if Statement • To execute more than one statement as part of an if statement, enclose them in { }: if (score > 90) { grade = 'A'; cout << "Good Job!n"; } • { } creates a block of code 17
- 19. The if/else statement • Provides two possible paths of execution • Performs one statement or block if the expression is true, otherwise performs another statement or block. • General Format: if (expression) statement1; // or block else statement2; // or block 19
- 20. if/else-What Happens To evaluate: if (expression) statement1; else statement2; • If the expression is true, then statement1 is executed and statement2 is skipped. • If the expression is false, then statement1 is skipped and statement2 is executed. 20
- 22. The if/else statement and Modulus Operator in Program 4-8 22
- 23. Flowchart for Program 4-8 Lines 14 through 18 23
- 24. Testing the Divisor in Program 4-9 Continued… 24
- 25. Testing the Divisor in Program 4-9 25
- 26. The if/else if/else statement • General Format: if (expression) statement1; // or block1 else if (expression) statement2; // or block2 else statement3; // or block2 26
- 27. The if/else if/else statement 27
- 28. The if/else if/else statement 28
- 30. Nested if Statements • An if statement that is nested inside another if statement • Nested if statements can be used to test more than one condition 30
- 31. Flowchart for a Nested if Statement 31
- 35. 4.6 The if/else if Statement 35
- 36. The if/else if Statement • Tests a series of conditions until one is found to be true • Often simpler than using nested if/else statements • Can be used to model thought processes such as: "If it is raining, take an umbrella, else, if it is windy, take a hat, else, take sunglasses” 36
- 37. if/else if Format if (expression) statement1; // or block else if (expression) statement2; // or block . . // other else ifs . else if (expression) statementn; // or block 37
- 38. The if/else if Statement 38
- 39. Using a Trailing else to Catch Errors • The trailing else clause is optional, but it is best used to catch errors. This trailing else catches invalid test scores 39
- 40. 4.7 Flags 40
- 41. Flags • Variable that signals a condition • Usually implemented as a bool variable • Can also be an integer – The value 0 is considered false – Any nonzero value is considered true • As with other variables in functions, must be assigned an initial value before it is used 41
- 43. Logical Operators • Used to create relational expressions from other relational expressions • Operators, meaning, and explanation: && AND New relational expression is true if both expressions are true || OR New relational expression is true if either expression is true ! NOT Reverses the value of an expression – true expression becomes false, and false becomes true 43
- 44. Logical Operators-Examples int x = 12, y = 5, z = -4; (x > y) && (y > z) true (x > y) && (z > y) false (x <= z) || (y == z) false (x <= z) || (y != z) true !(x >= z) false 44
- 45. The logical && operator 45
- 46. The logical || Operator 46
- 48. Checking Numeric Ranges with Logical Operators • Used to test to see if a value falls inside a range: if (grade >= 0 && grade <= 100) cout << "Valid grade"; • Can also test to see if value falls outside of range: if (grade <= 0 || grade >= 100) cout << "Invalid grade"; • Cannot use mathematical notation: if (0 <= grade <= 100) //doesn’t work! 48
- 50. The Conditional Operator • Can use to create short if/else statements • Format: expr ? expr : expr; x<0 ? y=10 : z=20; First Expression: Expression to be tested 2nd Expression: Executes if first expression is true 3rd Expression: Executes if the first expression is false 50
- 51. The Conditional Operator • The value of a conditional expression is – The value of the second expression if the first expression is true – The value of the third expression if the first expression is false • Parentheses () may be needed in an expression due to precedence of conditional operator 51
- 54. The switch Statement • Used to select among statements from several alternatives • In some cases, can be used instead of if/else if statements 54
- 55. switch Statement Format switch (expression) //integer { case exp1: statement1; case exp2: statement2; ... case expn: statementn; default: statementn+1; } 55
- 58. switch Statement Requirements 1) expression must be an integer variable or an expression that evaluates to an integer value 2) exp1 through expn must be constant integer expressions or literals, and must be unique in the switch statement 3) default is optional but recommended 58
- 59. switch Statement-How it Works 1) expression is evaluated 2) The value of expression is compared against exp1 through expn. 3) If expression matches value expi, the program branches to the statement following expi and continues to the end of the switch 4) If no matching value is found, the program branches to the statement after default: 59
- 60. break Statement • Used to exit a switch statement • If it is left out, the program "falls through" the remaining statements in the switch statement 60
- 61. break Statement – Not Used 61
- 62. break Statement - Used 62
- 63. break and default statements Continued… 63
- 64. break and default statements in Program 4-25 64
- 65. Using switch in Menu Systems • switch statement is a natural choice for menu-driven program: – display the menu – then, get the user's menu selection – use user input as expression in switch statement – use menu choices as expr in case statements 65