problem ： Input 30 Number , Output the maximum number
analysis
The first number may be the largest number , Remember it ;
For each subsequent number , Compare with the numbers you remember , If it's bigger than the number you remember , Then remember this number ;
After reading all the figures , Output the maximum number ;
loop
The phenomenon of doing something repeatedly in a program is called loop
For example, o 1~100 And , Find the average score of a class in a subject
Loop structure （ Cycle condition and cycle body ）
0x01 while loop
problem ： seek 1+2+3+4+……+100 Value
flow chart
Python Language implementation
= 0
= 1
i < 101: sum += i i += 1 print(sum)
problem ： seek 1~n And ,n For any positive integer
= int(input(' Please enter a positive integer n:'))
= 0
= 1
i < n+1: sum += i i += 1 print(sum)
0x02 for loop
Traversal cycle
For a data set
Loop through each element in the collection in turn
Is a certain number of cycles
for Circular statement syntax
range() function
range(start,end,step)
range() Function to create a sequence , Including the lower limit , Excluding upper limit
for example
range(101), Range 0~100
range(1,101), visit 1~100
problem ： seek 1~100 The sum of natural numbers between
sum = 0
for i in range(1,101):
sum += i
print(sum)
problem ： seek 1~n The sum of natural numbers between ,n For any positive integer
sum = 0
for i in range(1,101):
sum += i
print(sum)
0x03 A nested loop
Nesting of loops
It means to nest another complete loop in one loop , That is, the loop body also contains loop statements
while Circulation and for Loops can be nested with each other
Loop nested execution process An external circulation corresponds to a complete internal circulation
problem : Print 99 Multiplication table
# Print 99 Multiplication table
for i in range(1, 10): # The control line
for j in range(1, i + 1): # Control the column
print('{}*{}={}'.format(j, i, i * j), sep='', end='\t')
print()
0x04 break and continue
break To end the cycle
The program continues execution from the code after the loop
continue Used to end the current cycle
No longer execute the following undefined statements in the loop body
But don't end the current loop
problem ： seek 200 Endogenic quilt 17 The largest positive integer divided by
analysis ： This lookup process will iterate through... In a decreasing form 200~1 Integer between , When you find the first one that can be 17 The number of integral divisions , The cycle stops immediately
# seek 200 Endogenic quilt 17 The largest positive integer divided by
for i in range(200, 1, -1):
if i % 17 == 0:
break
print('200 Endogenic quilt 17 The largest positive integer to divide by is {}'.format(i))
problem ： seek 1~100 The sum of all even numbers within
# seek 1~100 The sum of all even numbers within
sum = 0
for i in range(1, 101):
if i % 2 == 0:
sum += i
else:
continue
print(sum)
problem ： Output 200 All prime numbers within , And output the number of primes
analysis ： Prime numbers are except 1 And a number that itself cannot be divided by other numbers , This question adopts double for Cycle to achieve , Outer traversal 2~200 All integers between , The inner loop is used to determine whether a number is a prime number
# Method 1
num = 0
for i in range(2, 200):
k = True
for j in range(2, i):
if(i % j == 0):
k = False
break
if(k==True):
print(i)
num += 1
print('200 Prime numbers within {} individual '.format(num))
# Method 2
import math
num = 0
for i in range(2, 200):
m = int(math.sqrt(i))
k = True
for j in range(2, m + 1):
if(i % j == 0):
k = False
break
if(k):
print(i)
num += 1
print('200 Prime numbers within {} individual '.format(num))
continue Statement and break The difference between sentences
continue Just end this cycle , Without terminating the execution of the entire loop
break Statement is to end the whole loop process , No longer judge whether the conditions of the cycle are true
