7.6. Looping and counting

The following program counts the number of times the letter “r” appears in a string:

Activity: CodeLens 7.6.1 (strCount)

This program demonstrates another pattern of computation called a counter. The variable count is initialized to 0 and then incremented each time an “r” is found. When the loop exits, count contains the result: the total number of r’s.

11-9-2: What is printed by the following:

s = "peanut butter"
count = 0
for char in s:
    if char == "t":
          count = count + 1
print(count)

• 0
• Incorrect! count is initialized to 0, but is then incremented by the for loop. Try again.
• 3
• Correct! The letter t appears 3 times in "peanut butter".
• 4
• Incorrect! The value of count is initially 0, not 1. Try again.
• Nothing, this is an infinite loop
• Incorrect! This for loop will eventually terminate because string s has a finite number of characters. Try again.

There are four errors in the following code. Fix the function so it takes a string and a character as arguments and returns the count of the character within the string.

def count(text, aChar): lettercount = 1 for c in text: if c = aChar: count = count + 1 return lettercount ==== from unittest.gui import TestCaseGui class myTests(TestCaseGui): def testOne(self): self.assertEqual(count('banana','a'),3,"Tested 'a' in 'banana'") self.assertEqual(count('pineapple','a'),1,"Tested 'a' in 'pineapple'") self.assertEqual(count('pepperoni pizza','p'),4,"Tested 'p' in 'pepperoni pizza'") self.assertEqual(count('racecar','r'),2,"Tested 'r' in 'racecar'") myTests().main()

In line 2, lettercount should be initialized to 0. In line 4, there should be a ==, not a =. In line 5, the variable name should be changed to lettercount. In line 6, the return statement should be indented.

def count(text, aChar): lettercount = 0 for c in text: if c == aChar: lettercount = lettercount + 1 return lettercount

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