Programming

The project is created to learning Javascript and Python3, but beginning with C++ on Tsinghua X_2015_T2, I wrote down the notes reference from MichaelLiao and some demos during learning to review later!  

Text editor：1. Dev-C++ 2. Visual Studio Code 3. Notepad ++

Also welcome to visit the Programming_CN!

Ⅰ. Knowledge Point    

Attention: 
	
	1. All of the languages below is sensitive to case;
	
	2. ';' indicates that the end of a sentence;
	
	3. Please indent with "Tab" key or 4 keyboard instead;

1. C++

Tip:

	Attention to priority of opertators.

1.1 The meaning of program design:

	#include <iostream>  // include library functions
	using namespace std; // namespace 
	/* the main function */
	int main() {
	
		return 0;
	}

2. Javascript

2.1 Data Type:

(1) Number:

• no distinction between int and float;
• NaN, standing for 'Not a Number', is used when sentences can not be computed!
• Infinity represents much great number, when used in case that the number exceed maximum!

	0 / 0; // NaN
	2 / 0; // Infinity

(2) String:

(3) Boolean: true false

* Operators:

1. && 'and', || 'or', ! 'not';

2. Comprision operators:　> >= < <= == ===

	* == could transfer the data type automatically and then compare them, so we have better using === to do comparision.
	
	* NaN is equal to nothing included itself:
	
		NaN === NaN; // false
		
	the only way to judge it is to use the function named isNaN():
	
		isNaN(NaN); // true
		
	* float comparision:
	
		1/3 === (1 - 2/3); // false
		
	Opps! the right way is to compute ABS of their difference and then to compare with a threshold:
	
		Math.abs(1/3 - (1 - 2/3)) < 0.0000001; // true

(4) null, undefined

* null, 0, ''

1. null is represented data which value is nothing, and it is associated with None in Python;

2. 0 is a number;

3. '' is a string which length is 0.

* undefined means that data has not defined;

* Usually, we prefer to use null unless we have to judge whether premeters of function have delivered.

(5) Array:

* Odered sets, could contains all type of data.

* Ways to make a array:

	1. [a, b];
	2. new.Array(a, b);
	
for better readability code, we highly recommended to use the formmer to create a array.

* Access: using index

		arr[0]; // visit the 1st element. output: a
		arr[2]; // undefined

3. Python3  

Ⅱ. Demos

1/33. Shopping

Description:

                       |    *price*    >>> *amount*
           *Tomatos*   | ￥7.9 yuan/kg >>>  0.8kg
           *Eggs*      | ￥9.5 yuan/kg >>>  1.5kg
           *Cucumbers* | ￥8.7 yuan/kg >>>  0.6kg

Question: How much the total vegetables?

C++ edition

#include <iostream>
using namespace std;

int main()
{
   cout << 7.9 * 0.8 + 9.5 * 1.5 + 8.7 * 0.6 << endl;
   return 0;
}

Python3 edition

print(7.9 * 0.8 + 9.5 * 1.5 + 8.7 * 0.6)

Javascript edition

console.log(7.9 * 0.8 + 9.5 * 1.5 + 8.7 * 0.6)

2/33.