Class One

:material-circle-edit-outline: 约 368 个字 :fontawesome-solid-code: 9 行代码 :material-clock-time-two-outline: 预计阅读时间 4 分钟

Intro¶

The first program

C++
    #include <iostream>  
    using namespace std;  
    int main()  
    {
        cout << "Hello, World!"<< endl;  

    }  

iostream is a header file name without a .h suffix. iostream.h happens to exist, yet it is an outdated version
<<: inserter
cin >> variable: extractor
use ; to connnect the shell commands

#include <iomanip>: manipulators are special functions that can be included in the I/O statement to alter the format parameters of a stream.
endl is one of them
setw(int width): set the output width
setprecision(int n): set the number of digits in decimal parts

#include <string>: c don't have a string type
string str: a string
str="Hello" , str("Hello"), s3{"see see"} for every type, yet when it comes to the third way of initialization, one should add g++ -std=c++11 when compiling.
objects can transfer contents through =
cin: only read the first word
getline(cin, str): read the whole line
string s[0]: the first character of the string, the same as the array in c
string s2=string s1+ string s3: string concatenation
s2.length(): the length of the string
s2(s3,2,3): the third to the fifth character of s3, 2 is the starting position, 3 is the length of the substring
s2.substr(2,3): the same as above
insert(size_t pos, const string& str): insert a string into another string
erase(size_t pos, size_t len): erase a substring
replace(size_t pos, size_t len, const string& str): replace a substring with another string
find(const string& str, size_t pos=0): find the first occurrence of a substring
append(const string& str): append a string to another string
string *p=&s: a pointer to a string
s->length(): the length of the string, the same as (*s).length()
string s1, s2; s1=s2;: copy the string, two different objects
string *p=&s1; string *q=&s2; p=q;: two pointers point to the same object s2