Python: Selection Damian Gordon. Python: Selection We’ll consider two ways to do selection: The IF statement The CASE statement.

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Presentation transcript:

Python: Selection Damian Gordon

Python: Selection We’ll consider two ways to do selection: The IF statement The CASE statement

Python: IF statement Damian Gordon

Python: IF statement In Python the general form of the IF statement is as follows: if CONDITION: STATEMENT(S) else: STATEMENT(S)

Python: IF statement But we’ll do: if CONDITION: # THEN STATEMENT(S) else: STATEMENT(S) # ENDIF;

# PROGRAM SimpleIfStatement: x = 6 y = 7 if x > y: # THEN print(“x is bigger”) else: print(“y is bigger”) # ENDIF; # END.

Python: IF statement Let’s get the user to input the values of x and y:

# PROGRAM AnotherSimpleIfStatement: x = int(input()) y = int(input()) if x > y: # THEN print(x, “is bigger than”, y) else: print(y, “is bigger than”, x) # ENDIF; # END.

Python: IF statement Let’s add some PRINT statements to make this clearer:

# PROGRAM AnotherSimpleIfStatementPrints: print(“Please input the first value”) x = int(input()) print(“Please second the second value”) y = int(input()) if x > y: # THEN print(x, “is bigger than”, y) else: print(y, “is bigger than”, x) # ENDIF; # END.

Python: IF statement We can make this shorter:

# PROGRAM AnotherSimpleIfStatementPrintsShorter: x = int(input(“Please input the first value\n”)) y = int(input(“Please second the second value\n”)) if x > y: # THEN print(x, “is bigger than”, y) else: print(y, “is bigger than”, x) # ENDIF; # END.

Python: IF statement Lets try the Odd or Even program:

# PROGRAM IsOddOrEven: x = int(input(“Please input the number\n”)) if (x % 2) != 0: # THEN print(x, “is odd”) else: print(x, “is even”) # ENDIF; # END.

OperatorDescription != is not equal to == is equal to > is greater than < is less than >= is greater than or equal to <= is less than or equal to

Python: IF statement Let’s try the bigger of three numbers:

# PROGRAM BiggerOfThree: a = int(input(“Please input the first value\n”)) b = int(input(“Please second the second value\n”)) c = int(input(“Please second the third value\n”)) if a > b: # THEN if a > c: # THEN print(a, “is bigger than”, b, “ and ”, c) else: print(c, “is bigger than”, a, “ and ”, c) # ENDIF; else: if b > c: # THEN print(b, “is bigger than”, a, “ and ”, c) else: print(c, “is bigger than”, a, “ and ”, b) # ENDIF; # END.

Python: CASE statement Damian Gordon

Python: CASE statement Python doesn’t support a CASE statement But it does have a special form of IF statement that uses ELIF instead of ELSE.

# PROGRAM BiggerOfThree: a = int(input(“Please input the first value\n”)) b = int(input(“Please second the second value\n”)) c = int(input(“Please second the third value\n”)) if a > b: # THEN if a > c: # THEN print(a, “is bigger than”, b, “ and ”, c) else: print(c, “is bigger than”, a, “ and ”, c) # ENDIF; else: if b > c: # THEN print(b, “is bigger than”, a, “ and ”, c) else: print(c, “is bigger than”, a, “ and ”, b) # ENDIF; # END.

# PROGRAM BiggerOfThree: a = int(input(“Please input the first value\n”)) b = int(input(“Please second the second value\n”)) c = int(input(“Please second the third value\n”)) if a > b: # THEN if a > c: # THEN print(a, “is bigger than”, b, “ and ”, c) else: print(c, “is bigger than”, a, “ and ”, c) # ENDIF; else: if b > c: # THEN print(b, “is bigger than”, a, “ and ”, c) else: print(c, “is bigger than”, a, “ and ”, b) # ENDIF; # END.

# PROGRAM BiggerOfThreeElif: a = int(input(“Please input the first value\n”)) b = int(input(“Please second the second value\n”)) c = int(input(“Please second the third value\n”)) if a > b: # THEN if a > c: # THEN print(a, “is bigger than”, b, “ and ”, c) else: print(c, “is bigger than”, a, “ and ”, c) # ENDIF; elif b > c: # THEN print(b, “is bigger than”, a, “ and ”, c) else: print(c, “is bigger than”, a, “ and ”, b) # ENDIF; # END.

Python: IF-ESIF statement In Python the general form of the IF-ESIF statement is as follows: if CONDITION: STATEMENT(S) elif CONDITION: STATEMENT(S) elif CONDITION: STATEMENT(S) else: STATEMENT(S)

Python: IF-ESIF statement But we’ll do: if CONDITION: # THEN STATEMENT(S) elif CONDITION: # THEN STATEMENT(S) elif CONDITION: # THEN STATEMENT(S) else: STATEMENT(S) # ENDIF;

Python: IF-ESIF statement Let’s look at doing a multi-choice question program:

# PROGRAM MultiChoiceQuestion: InputValue = input("Please input your answer:\n") if InputValue == "a": # THEN print("Wrong Answer") elif InputValue == "b": # THEN print("Wrong Answer") elif InputValue == "c": # THEN print("Right Answer") elif InputValue == "d": # THEN print("Wrong Answer") else: print("Bad Option") # ENDIF; # END.

Python: IF-ESIF statement Here’s how to calculate a grade:

# PROGRAM GetGrade: InputValue = int(input("Please input the first value\n")) if InputValue >= 70: # THEN print("It's a first") elif InputValue >= 60: # THEN print("It's a 2.1") elif InputValue >= 50: # THEN print("It's a 2.2") elif InputValue >= 40: # THEN print("It's a third") else: print("Dude, sorry, it's a fail") # ENDIF; # END.

etc.