<!--introduction-->
# 10/4 第四堂社課
## 今日講師：R緯
#### (Python班)
---
# 今日課程主題：
----
# for迴圈
(for loop)
----
# 快速複習
----
## 例題1-複習
----
```python=
N = int(input())
a = 1
while N != 1:
if N%2 == 1:
N = 3*N + 1
else:
N = N//2
a += 1
print(a)
```
---
<!--for loop-->
# for迴圈
(for loop)
----
## for [變數] in [序列]:
(for [variable] in [sequence]:)
----
## What is a sequence???
----
## 補充:
## 陣列(Array), range()... ∈
## 序列(sequence)
串列(List), 元組(Tuple), 字典(Dictionary), 集合(Set)
∈ 陣列(Array)
----
# range()函式
----
## range(開始, 結束, 步長)
range(start, stop, step)
----
## 從start 開始。預設為0。
## 到stop 結束，但不包括stop。
## step 步長，預設為1。
----
## 三項parameter:
range(start, stop, step)
```python=
for i in range(2, 7, 3):
print(i, end="")
```
output
```python
25
```
----
## 二項parameter:
range(start, stop) ≡ range(start, stop, 1)
step預設為1
```python=
for i in range(2, 7):
print(i, end="")
```
output
```python
23456
```
----
## 一項parameter:
range(stop) ≡ range(0, stop, 1)
step預設為1, start預設為0
```python=
for i in range(7):
print(i, end="")
```
output
```python
0123456
```
----
## for和while都是迴圈
## 因此break, continue, pass也可以在for中
---
## 例題二-示範
----
```python=
N = int(input())
R = int(input())
a = N
for i in range(1, R):
a *= (N-i)
print(a)
```
----
## 例題三~五
---
# END
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