麻省理工学院公开课：计算机科学及编程导论 课堂笔记
6.00
lecure1
skill goals:
1. computational thinking
2.read and write code
3.solve problem
think like a computational scientist
what is computaion?
python：三个维度来看：
high-level or low level language
general or targeted language
编译语言 or 解释语言
语法 syntax： what are legal expression in this language
语义 static semantics: what programs are meaningful
full semantics: what does the program meaning; what happen when running python
data
numbers
integer (INT)
floating point
strings
'abc'
表达式expression
3**5 次方；3/5=0；3.0/5浮点数；
为一个变量命名 value='eric' 绑定；
lecture 2
data
value and type
combine in expressions: ooperands and operators 运算符和运算对象
interpreter解释器 : evaluate and print
script 脚本: no print unless explict 除非我们让它这么做
str(3)+'abc' str: 变成字符串
type checking : weak or strong
4<'3' 没有报错，但是无意义
typing discipline 规范
运算前规定数据类型
9/5=1
9%%5=4
operate precedence操作优先 乘除>加减
when in double ，use parents括号
赋值 assignment 绑定binding 变量 linking to a 值
变量 variable X=3 used anywhere leghal
类型 is 动态的 X='ABC' 不要反复改变变量的类型
statements 声明 : legal commands that python can interpret
comments 注释 帮助reader理解代码的含义
变量名称的选择 ： 评价是否优秀的代码 excluded key words
line programs : run one by one
branching programs : can change the order of instructions based on tests
： colon冒号 定义指令集/指令集的开始；回车意味着指令集的结束
x=15#把等号左边的值绑定到右边的变量
if (x/2)*2 ==x : #==判断左边的值是否等于右边
print 'even'
else: print 'odd'
if
block of instructions
else:
block of instructions
if 可以嵌套
x=15
y=13
z=11
print x,y,z
if x
if x
else:print'z is least'
else: print 'y is least'
#is this right?
if x
elif y
else: print'z is least'
计算复杂度-算法种类
iteration or loops 迭代 或者循环
y=0
x=3
itersLeft=x
while(itersLeft>0): y=y+x
itersLeft=itersLeft-1
#求数的平方
print y
循环内必须有会变化的量
写代码前一定要搞清楚对输入值的期望