01 - fundamentals

fundamentals

If someone claims to have the perfect programming language, he is either a fool or a salesman or both.
要是有人说有完美的编程语言，那这货要么是个傻der，要么是个卖课的，要么是个卖课的傻der。
– Bjarne Stroustrup, Inventor of C++

C++ 优劣

benefits 优势

• C++ is fast
  C++是编译型语言，python是解释型语言。
  Get ready for the Python vs C++ speed showdown during Assignment 1!

• C++ is popular
  许多公司和研究项目都使用 C++，并且在 C++ 中进行编码面试是很常见的

• C++ is powerful
  C++ brings you closer to the raw computing power that your computer has to offer

drawbacks 劣势

• C++ is complex
  · We will rely on the Stanford C++ libraries to provide a friendlier level of abstraction
  · In the future, you may choose to explore the standard libraries

• C++ can be dangerous
  "With great power comes great responsibility"

Comments 注解

• Single-line comments

  // Two forward slashes comment out the rest of the line
  cout << "Hello, World!" << endl; // everything past the double-slash is a comment
  

• Multi-line comments

  /* This is a multi-line comment.
   * It begins and ends with an asterisk-slash.
   */
  

Includes 引用

• Utilizing code written by other programmers is one of the most powerful things that you can do when writing code.

• In order to make the compiler aware of other code libraries or other code files
  that you want to use, you must include a header file. There are two ways that
  you can do so:
  #include <iostream>

  • Use of the angle bracket operators is usually reserved for code from the C++ Standard library

  #include "console.h"

  • Use of the quotes is usually reserved for code from the Stanford C++ libraries, or code in files that you have written yourself

Console Output

• In C++, the way that you get information to the console is by using the cout keyword and angle bracket operators (<<).
• The endl is necessary to put the cursor on a different line. Here is an example with and without the endl keyword.

cout << "The answer to life, the universe, and everything is " << 42 << "." << endl;

Variables and Types

Variables

• 一个变量存储一个对应的值

  A way for code to store infomation by associating a value with a name.

• We will think of a variable as a named container storing a value.

106 className

16.3 sundayTemp

• 变量是编程中最基础的部分之一
• 注意⚠️: c++ 使用驼峰式命名变量

Types

// int
int a = 1;
// double
double b = 3.14;
// string
string s = "hello";
// char
char c = 'A';

double a = 4.2; // ERROR! You cannot redifine a variable to be another type
int a = 12; // ERROR! You do not need the type when re-assigning a variable
a = 12; // this is okay, updates variable value

• In C++, all types must be explicitly defined when the variable is created, and a variable cannot change its type.

Functions and Parameters

Anatomy of a function

// function prototype
returnType functionName(varType parameter1, varType parameter2, ...);
// function defination
returnType functionName(varType parameter1, varType parameter2, ...) {
    returnType variable = /* Some fancy code. */
    /* Some more code to actually do things. */
    return variable;
   }

// example
double average(double a, double b){
   double sum = a + b;
   return sum / 2;
}
int main(){
   double mid = average(10.6, 7.2);
   cout << mid << endl;
   return 0;
}

Pass by Value

#include<iostream>
using namespace std;
int doubleValue(int x) {
	x *= 2;
	return x;
}
int main() {
    int myValue = 5;
    int result = doubleValue(myValue);
    cout << "myValue: " << myValue << " ";
    cout << "result: " << result << endl;
}

// answer:
// myValue: 5 result: 10

Control Flow

Boolean Expressions

Expression	Meaning	Operation	Meaning
a < b	a is less than b
a <= b	a is less than or equal to b	a && b	Both a AND b are ture
a > b	a is greater than than b	a || b	Either a OR b are ture
a >= b	a is greater than or equal to b	!a	If a is true, returns false, and vice-versa
a == b	a is equal to b
a != b	a is not equal to b

Conditional Statements

• The C++ if statement tests a boolean expression and runs a block of code if the expression is true, and, optionally, runs a different block of code if the expression is false. The if statement has the following format:

if(expression) {
	statements if expression is true
} else {
	statements if expression is false
}

• Additional else if statements can be used to check for addtional conditions as well

if(expression1) {
	statements if expression1 is true
} else if(expression2) {
	statements if expression2 is false
} else {
	statement if neither expression1 nor expression2 is true
}

while loops

• Loops allow you to repeat the execution of a certain block of code multiple times
• while loops are great when you want to continue executing something until a certain condition is met and you don't know exactly how many times you want to iterate for

// Execution continues until expression evaluates to false
while (expression) {
	statement;
	statement;
	...
}

for loops

• for loops are great when you have a known, fixed number of times that you want to execute a block of code

/*
 * The initializationStatement happens at the beginning of the loop, and initializes a variable. E.g., int i = 0.
 * 
 * The testExpression is evaluated initially, and after each run through the loop, and if it is true, and the loop continues for another iteration. E.g., i < 3.
 * 
 * The updateStatement happens after each loop, but before testExpression is evaluated. E.g., i++.
 */
for (initializationStatement; testExpression; updateStatement) {
        statement;
        statement;
        ...
}

Testing

Software and cathedrals are much the same – first we build them, then we pray.
– Sam Redwine