User input and output and while loop

1. Use the function input() to input and print() to print. Strings can be separated by commas. end=‘ ’ keyword parameter, you can print without line breaks, sep=‘ the delimiter you want’, keyword parameter, replace the default delimiter string.

2. The input is Input and the output is Output. Therefore, we collectively call input and output Input/Output, or abbreviated as IO. Interactive programs can be written by taking user input and learning to control when the program runs.

3. The function input() allows the program to pause and wait for the user to input some text. After getting user input, Python stores it in a variable for your convenience.

4. Whenever you use the function input(), you should specify a clear and easy-to-understand prompt that accurately indicates what information you want the user to provide - any prompt that indicates that the user should enter any information OK.

5. You can store the prompt in a variable and then pass the variable to the function input()

prompt = "If you tell us who you are, we can personalize the messages you see."

prompt += "\nWhat is your first name? " # String addition

name = input(prompt)

Operator += Appends a string to the end of the string stored in prompt.

7.1 Use int() to input numbers

Because the data type returned by input() is str (string), python will convert the directly input number into a string. str cannot be directly compared with an integer, str must be converted to an integer first. Python provides the int() function to accomplish this

height = input("How tall are you, in inches? ")

height = int(height) #Convert to integer

7.2 Modulo operator

When processing numerical information, the modulo operator ( %) is a useful tool that divides two numbers and returns the remainder:

>>> 4 % 3

1

> >> 5 % 3

2

>>> 6 % 3

0

>>> 7 % 3

1

If one number is divisible by another number, the remainder is 0, so the modulo operator will return 0. You can use this to determine whether a number is odd or even.

7.3 while loop

The for loop is used to create a block of code for each element in the collection, while the while loop runs continuously until the specified condition is not met.

1 current_number = 12 while current_number < 5:3     print(current_number)4     current_number +=1

7.3.1 Using flags

True and False, Boolean operators and while loops can be used together to implement complex logic.

7.3.2 Use break to exit the loop

7.3.3 Use continue in the loop

 1 current_number = 0 2  3 while current_number < 10: 4  5     current_number += 1 6  7     if current_number % 2 == 0: 8  9     continue10 11     print(current_number)

If the result is 0 (meaning current_number can be 2), execute the continue statement, causing Python to ignore the rest of the code and return to the beginning of the loop. If the current number is not divisible by 2, the rest of the code in the loop is executed and Python prints the number.

Loops are an effective way to make computers do repetitive tasks.

The break statement can directly exit the loop during the loop, while the continue statement can end the current cycle in advance and directly start the next cycle. These two statements must usually be used in conjunction with the if statement.

Pay special attention not to abuse break and continue statements. Break and continue will cause too many forks in code execution logic and are prone to errors. Most loops do not need to use break and continue statements. In the two examples above, break and continue statements can be removed by rewriting the loop conditions or modifying the loop logic.

7.3.4 Avoid infinite loops

Sometimes, if the code is written incorrectly, the program will fall into an "infinite loop", that is, it will loop forever. At this time, you can use Ctrl+C to exit the program, or force the Python process to end.

7.4 Use while loops to process lists and dictionaries

The for loop is an effective way to traverse the list, but the list should not be modified in the for loop, otherwise it will be difficult for Python to track the items in it. element. To modify a list while iterating over it, use a while loop. By combining while loops with lists and dictionaries, you can collect, store, and organize large amounts of input for later review and display.

7.4.1 Move elements between lists

By using a while loop, the function pop() deletes the last element and append() adds the element

7.4.2 Delete the containing All elements of a specific value

Implemented through while loop and remove()

7.4.3 Use user input to populate the dictionary

responses[name] = response

Need to define a dictionary

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