Branch and loop

Process control - controls the sequence of code execution

1. Sequential structure: the code is executed from top to bottom, and each statement is executed only once. (default)

2. Branch structure: select whether to execute or not to execute part of the code according to the conditions. (use if)

   age = int (input("Please enter your age:" ))
   if age >= 18:
       print ("adult")
   else:
   print("under age")
   

3. Loop structure: make the code execute repeatedly (for, while)

   # for loop
   for _ in rang(10):
       print("Xiao Zhou")
   

if branch structure

1. If single branch structure - if... Just...

   Syntax:

   if Conditional statement :
   	Code snippet (code that will be executed only if conditions are met)
   

   Problem solving: perform an operation when the conditions are met, and do not perform it when the addition is not met.

   explain:

   if -- keyword, fixed writing method

   Conditional statement - any expression with results, including: specific data, operation expression (except assignment operation), assigned variable and function call expression

   : -- Fixed writing method

   Code segment -- structurally, it is one or more statements (at least one) that maintain an indent with if;

   Logically, a code segment is a code that will be executed only when the condition is established

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   #If the data saved by the variable is an integer, print 'Integer'
   num = 33
   if type(num) == int :
       print("integer")
   

   # Print 'pass' according to score
   score = float(input("Please enter your grade:"))
   if score >= 60.0:
       print("Qualified results")
   

2. If double branch structure - if... Then... Otherwise

   Application scenario: perform an operation when a condition is met, and perform another operation when the condition is not met

   Syntax:

   if Conditional statement:
   	Code snippet 1 (code to be executed if conditions are met)
   else:
   	Code segment 2 (code to be executed when conditions are not met)
   

   #If the data saved by the variable is an integer, print 'Integer'
   num = 33
   if type(num) == int :
       print("integer")
   else:
       print("Not an integer")
   

   # Print 'pass' according to score
   score = float(input("Please enter your grade:"))
   if score >= 60.0:
       print("Qualified results")
   else:
       print("Unqualified results")
   

   # Judge the parity of an integer
   #Method 1:
   num = int(input("Please enter an integer:"))
   if num % 2 == 0:
       print(num,"It's an even number",sep='')
   else:
       print(num,"It's an odd number",sep='')
   #Method 2:
   num = int(input("Please enter an integer:"))
   if num % 2:			#A remainder of 1 represents True and a remainder of 0 represents False
       print(num,"It's an odd number",sep='')
   else:
       print(num,"It's an even number",sep='')
   

3. If multi branch structure - if... If... If... If... If... Otherwise

   Application scenario: perform different operations according to different conditions

   Syntax:

   if Condition 1:
   	Code snippet 1
   elif Condition 2:
   	Code snippet 2
   elif Condition 3:
   	Code snippet 3
   ...						# elif can be any number; else can have or not
   else: 
   	Code snippet N
   

   #   Print scholarship amount based on score 
   # Method 1: after this method is completed, it will continue to judge the following operations
   	# Main solution: do different things according to different conditions
   score = float(input("Please enter your grade:"))
   if score > 90:
       print(2000)
   if 85< score <=90:
       print(1000)
   if 75 < score <=85:
       print(500)
   if 60 <= score <75:
       print(200)
   else:
       print(0)
   # Method 2:
   	# The main solution: do different things according to different conditions, but require the relationship between conditions. One condition holds, and the other condition never holds.
   score = float(input("Please enter your grade:"))
   if 90 < score:
       print(2000)
   elif 85 < score:
       print(1000)
   elif 75 < score:
       print(500)
   elif 60 <= score:
       print(200)
   else:
       print(0)
   

for loop

1. Syntax:

   for variable in sequence:
       Circulatory body (Code to execute)
   

   Description: for - keyword; Fixed writing

   Variable - valid variable name (can be defined or undefined)

   in - keyword; Fixed writing

   Sequence - data of container data type; Container data types include string, list, dictionary, tuple, iterator, generator, range, etc.

   Loop body - one or more statements that maintain an indentation with for; The loop body is the code that needs to be executed repeatedly.

   Execution process: let variables take values from the sequence one by one until they are finished; Take a value and execute the loop body once

   The number of cycles of the for loop is related to the number of elements in the sequence.

2. range function -- creates an arithmetic sequence (integer)

   range(N) --- # Generate an equal difference sequence of [0,N), and the difference is 1 
   range(M,N) --- # Generate an equal difference sequence of [M,N), and the difference is 1
   range(M,N,step) --- #Generate an equal difference sequence of [M,N), and the difference is step
   range(1,10,2) ---> # 1,3,5,7,9
   

3. Two application scenarios:

   ① Cumulative summation:

   #Write code for 1 + 2 + 3 ++ Sum of 100
   #Method 1
   result = 0
   for i in range(1,101):
       result = result + i
       if i == 100 :
           print(result)
   #Method 2
   result = 0 
   for x in range(1,101):
       result += x
   print(result)
   

   # Factorial of 10
   #Method 1
   result = 1
   for i in range(1,11):
       result = result * i
       if i == 10 :
           print(result)
   #Method 2
   result = 1
   for i in range(1,11):
       result *= i
   print(result)
   

   ② Number of Statistics:

one
result = 1
for i in range(1,11):
result = result * i
if i == 10 :
print(result)
#Method 2
result = 1
for i in range(1,11):
result *= i
print(result)

② Number of Statistics: