Sample Paper 2 by Teachoo

Computer Science - Class 11
Teachoo Sample Paper

## ``` print("The number of times each character appears in the string is", char_frequency(string)) ```

### Answer by student

``` def char_frequency(string): ```

```     freq = {} ```

```     for char in string: ```

```         # Check if the character is already in the dictionary ```

```         if char in freq: # Missing statement 1 ```

```             # Increment the value of the character by 1 ```

```             freq[char] += 1 # Missing statement 2 ```

```         else: ```

```             # Add the character as a key and 1 as its value to the dictionary ```

```             freq[char] = 1 # Missing statement 3 ```

```     # Return the dictionary ```

```     return freq # Missing statement 4 ```

``` string = input("Enter a string: ") ```

``` print("The number of times each character appears in the string is", char_frequency(string)) ```

### Detailed answer by teachoo

• The char_frequency function takes a string as an argument and returns a dictionary that maps each character to its frequency in the string.
• To create an empty dictionary, we use freq = {} .
• To loop through each character in the string, we use for char in string: . This will assign each character to the variable char one by one.
• To check if a character is already in the dictionary, we use if char in freq: . This will return True if char is a key in freq , False otherwise. This will be statement 1.
• To increment the value of a character by 1, we use freq[char] += 1 . This is equivalent to freq[char] = freq[char] + 1 . This will add 1 to the current value of freq[char] and assign it back to freq[char] . This will be statement 2.
• To add a character as a key and 1 as its value to the dictionary, we use freq[char] = 1 . This will create a new entry in freq with char as the key and 1 as the value. This will be statement 3.
• To return the dictionary, we use return freq . This will exit the function and send back freq as the output. This will be statement 4.
• To take a string as input from the user, we use string = input("Enter a string: ") . This will display "Enter a string: " on the screen and wait for the user to enter some text. The text entered by the user will be stored as a string in the variable string .
• To print the number of times each character appears in the string using the char_frequency function, we use print(“The number of times each character appears in the string is”, char_frequency(string)) . This will call the char_frequency function with string as an argument and print its return value along with some text.

So, the final code is:

``` # A function that returns a dictionary that maps each character to its frequency in a string ```

``` def char_frequency(string): ```

```     # Initialize an empty dictionary ```

```     freq = {} ```

```     # Loop through each character in the string ```

```     for char in string: ```

```         # Check if the character is already in the dictionary ```

```         if char in freq: # Missing statement 1 ```

```             # Increment the value of the character by 1 ```

```             freq[char] += 1 # Missing statement 2 ```

```         else: ```

```             # Add the character as a key and 1 as its value to the dictionary ```

```             freq[char] = 1 # Missing statement 3 ```

```     # Return the dictionary ```

```     return freq # Missing statement 4 ```

``` # Take a string as input from the user ```

``` string = input("Enter a string: ") ```

``` # Print the number of times each character appears in the string using the char_frequency function ```

``` print("The number of times each character appears in the string is", char_frequency(string)) ```