Control Flow

Ha Khanh Nguyen (hknguyen)

• 1. if Statement
• 2. elif Statement
• 3. else Statement
• 4. Exercises

---

1. if Statement

• The if statement checks a condition that, if True, evaluates the code in the block that follows:

if x < 0:
    print('It\'s negative!')

• Note that a colon : is needed at the if statement, before the code block begins.
• And the code block after : MUST BE INDENTED.
  • Jupyter Notebook automatically indent the code after a colon :.
  • If you want to manually indent a line of code, use TAB! Please avoid using the spacebar.

---

2. elif Statement

• An if statement can be optionally followed by one or more elif blocks.

if x < 0:
    print('It\'s a negative')
elif x == 0:
    print('Equal to zero')
elif 0 < x < 5:
    print('Positive but smaller than 5')

---

3. else Statement

• The else statement is used a catch-all block if all of the conditions above it are False.

if x < 0:
    print('It\'s a negative')
elif x == 0:
    print('Equal to zero')
elif 0 < x < 5:
    print('Positive but smaller than 5')
else:
    print('Positive and larger than or equal to 5')

• If any of the condition is True, no further elif or else blocks will be reached.

---

4. Exercises

Exercise 1: We are given 2 numbers stored in variables a and b. Write a program to print the number with the larger value.

Exercise 2: We are given 2 strings s1 and s2. If one is contained in the other, print "One is a substring of the other!". Otherwise, print "They are distinct strings!"