3 strings, containers, and arrays

1 character string string

Standard library type string Represents a variable length sequence of characters , Be careful , It is different from string literals .

Tips: character string string Examples different from string literals ： For example, in string splicing （+） When s1+s2 When using , Make sure at least one side is string type .string s1 = "hello" + "world" // error , Both sides are string literals , String splicing cannot be realized ！！！

1.1 character string string Some operations of

1、 initialization ：

Mode one ： Copy initialization （copy initialization）： Use equal sign = Copy an existing object to the object being created . for example string str1 = str2 perhaps string str = "1234" etc. .
Mode two ： Direct initialization （direct initialization）： Assign values to objects through parentheses . for example string str(s1) perhaps string str("value") etc. .

    string str2 = "i_am_second";
    string str2a = str2;
    str2a[0] = 'h';

    string str2b = "i_am_test";
    string str2c = " ";
    str2b = str2c;

    cout<<"------------The using of = in string--------------"<<endl;
    cout<<"str2 is: "<<str2<<endl<<"str2a is: "<<str2a<<endl;
    cout<<"str2b is: "<<str2b<<endl<<"str2c is: "<<str2c<<endl<<endl;

The output is ：------------The using of = in string--------------
str2 is: i_am_second
str2a is: h_am_second
str2b is:
str2c is:

2、 Find the length ： use str.size() perhaps str.length().

    string str1 = "i_am_first";

    // string The length of the type ;( use str.size() perhaps str.length())
    int len  = str1.size();cout<<"the size of str1 is: "<<len<<endl;
    int leng = str1.length();cout<<"the length of str1 is: "<<leng<<endl<<endl;

The output is ：the size of str1 is: 10 and the length of str1 is: 10.

3、 String splicing ： Directly through the operator +, It is worth noting that ,+ At least one of the two objects of No. must be string Type of .

    cout<<"------------The using of + in string--------------"<<endl;
    string str3 = "i_am_";
    string str3a = "third";
    string str3b = str3 + str3a ;
    cout<<"str3 is: "<<str3<<endl<<"str3a is: "<<str3a<<endl<<"str3b is: "<<str3b<<endl<<endl;

The output is ：------------The using of + in string--------------
str3 is: i_am_
str3a is: third
str3b is: i_am_third

4、 String slice ：substr( Location , length )

    string str4 = "i_am_forth";
    string str4a = str4.substr(5,5);
    cout<<"------------slice of string type--------------"<<endl;
    cout<<"str4 is: "<<str4<<endl<<"str4a is: "<<str4a<<endl<<endl;

The output is ：------------slice of string type--------------
str4 is: i_am_forth
str4a is: forth

5、 Other operating ：

1.2 Yes string Character operations in objects

/* //---------------------------- Handle string The characters in -------------------------- */
    string str5 = "I_a m _5(fifth)";

    //  Determine whether the character is a number 
    bool isnum = isdigit(str5[7]);
    cout<<"------------Process the characters of the string--------------"<<endl;
    cout<<"5 in str5 is digit(1=true,0=false): "<<isnum<<endl;

    //  Determine whether the character is a letter 
    bool isalp = isalpha(str5[1]);
    cout<<"i in str5 is alpha(1=true,0=false): "<<isalp<<endl;

    //  Determine whether the character is uppercase 
    bool isup = isupper(str5[0]);
    cout<<"i in str5 is alpha(1=true,0=false): "<<isup<<endl;

    //  Determine whether the characters are lowercase 
    bool islo = islower(str5[2]);
    cout<<"i in str5 is alpha(1=true,0=false): "<<islo<<endl;

    //  Determine whether the characters are spaces and other symbols 
    bool isspa = isspace(str5[3]);
    cout<<"i in str5 is alpha(1=true,0=false): "<<isspa<<endl;

The output is ：------------Process the characters of the string--------------
5 in str5 is digit(1=true,0=false): 1
i in str5 is alpha(1=true,0=false): 0
i in str5 is alpha(1=true,0=false): 1
i in str5 is alpha(1=true,0=false): 1
i in str5 is alpha(1=true,0=false): 1

1.3 Example

Example 1： The string str5a Delete all spaces in the string of , Such as str5 = “i am str5a”; The final output "iamstr5"

Their thinking ：
1、 Press the subscript i Judge ,
2、 Record space subscripts i, Split it into two characters (0–i and i+1–end) String recombining ;
3、 The subscript in the space will be reset to... In the next traversal (i-1)

    for(int i = 0; i < str5a.size(); i++)
    {
    
        if(isspace(str5a[i]))
        {
    
            string str5b = str5a.substr(0,i);
            string str5c = str5a.substr(i+1);
            str5a = str5b + str5c;
            i--;
        }
    }
    cout<<"Example1--to delet the space in (i am str5a): "<<str5a<<endl<<endl;

The output is ：Example1–to delet the space in (i am str5a): iamstr5a

2 Containers vector And iterators

2.1 Containers

1、 initialization ： It is worth noting that , The element length of the container can be different vector<string> str = {"1","12","123"};

    // Define initialization , You can define elements of different lengths in a container 
    vector<string> str1 = {
    "1","12","123"};
    cout<<"---------------to init the vector type data--------------"<<endl;
    cout<<"str1={a,ab,abc} the str[1] is: "<<str1[1]<<endl<<endl;

The output is ---------------to init the vector type data--------------
str1={1,12,123} the 1 number is: 12

2、 Additive elements ：v.push_back(e) Add elements to the tail .

    //  Add elements to the end 
    str1.push_back("1234");
    cout<<"---------------add data in the end of vector --------------"<<endl;
    cout<<"str1={1,12,123,1234} the str1[3] is: "<<str1[3]<<endl<<endl;

The output is ---------------add data in the end of vector --------------
str1={1,12,123,1234} the 3 number is: 1234

3、 Other operating ：

Be careful ：vector object （ as well as string object ） Of Subscript operator [i], Subscript operations can only be performed on elements that are known to exist , Cannot be used to add elements . Both of the following are false ！！！

    string a = "";
    vector<int> b;

    for(int i = 0; i < 2; i++)
    {
    
        a[i] = char(i);
    }
    for(int i = 0; i < 2; i++)
    {
    
        b[i] = i;
    }

2.2 iterator

1、 Get the header and footer elements ： Head element direct *str.begin() that will do ; The tail element needs to move the tail iterator back one bit , Otherwise, a null pointer is passed , That is, the tail element *--str.end()

    //  Get the first and last elements of the iterator ; The tail element needs to be *--str.end(), Directly *str.end() It is usually a null pointer 
    string str2 = "hello_iterator";
    vector<string> str3 = {
    "abc","ab","a"};
    auto str2a = str2.begin();

    cout<<"-----------get the begin and end mumber in vector and string ----------"<<endl;
    cout<<"the str2={hello_iterator} first number is: "<<*str2a<<endl;

    auto str3a = str3.end();

    cout<<"the str3={abc,ab,a} end number[*--str3.end()] is: "<<*--str3a<<endl<<endl;

The output is ：-----------get the begin and end mumber in vector and string ----------
the str2={hello_iterator} first number is: h
the str3={abc,ab,a} end number[*–str3.end()] is: a

2、 Get the data in the container ： For example, in vector<string> str = {"abc","ab","a"};iter = str.begin() Be careful *iter[2] and (*iter)[2] The difference between , The former *iter[2]==str[0+2]; the latter (*iter)[2]==str[0][2].

    //  Some operations on iteration pointer 
    //  Get the elements in the string 
    auto str3b = str3.begin();
    cout<<"-----------get the data in iterator ----------"<<endl;
    cout<<"in str3={abc,ab,a} the str3c is: "<<*str3b<<endl;
    cout<<"in str3={abc,ab,a} the str3c[1] is(==str3[2]): "<<str3b[2]<<endl;
    cout<<"in str3c={abc} the (*str3c)[2] is(==str3[0][2]): "<<(*str3b)[2]<<endl;

The output is ：-----------get the data in iterator ----------
in str3={abc,ab,a} the str3c is: abc
in str3={abc,ab,a} the str3c[1] is(==str3[2]): a
in str3c={abc} the (*str3c)[2] is(==str3[0][2]): c

3、 Other operating ：

3.3 Array

1、 The length of the array must be const expression , Or don't write .

2、 Array does not allow direct assignment to another array .

int a[] = {
    1,2,3};
int b[] = a; // error 
int c[];
c = a;// error 

3.3.1 Complex array

1、 Array of pointer types （ Pointer array ）, keyword <type>* <var_name>, for example int *arrp[10], Express 10 individual int* Pointer array of type .

2、 Pointer to array （ Array pointer ）, keyword <type> (*<var_name>), for example int (*parr)[10] To point to 10 Pointer to an integer array .

Operator priority ： Assignment operator < Logical operators < Relational operator < Arithmetic operator < Brackets

int arr[10] = {
    1,2,3,4,5,6,7,8,9,0};
int *arrp[10];  //int An array of type pointers 
int (*parr)[10];    // Point to 10 Pointer to an array of integer elements 
// arrp = &arr; // error ！
parr = &arr;
cout<<parr<<endl;   // Output the first address of the array 
cout<<parr[0]<<endl;   // Output the first address of the array 
cout<<*parr[2]<<endl;   // Not the value of the output array , It's the decimal number of the address of the array , It is not recommended at all 
cout<<(*parr)[2]<<endl;   // The value of the output array 

3、 References to arrays , keyword <type> (&<var_name>), for example int (&refarr)[10] = arr Express 10 A reference to an integer array . Cannot define an array whose data type is a reference .

3.3.2 C Style string

1、 from C Inherited string , Use empty characters （\0） end .

2、 The relevant operation ：
①strlen(p)------ return p The length of , Empty characters are not counted ;

②strcmp(p1, p2)------ Compare p1 and p2 Equality of . If p1==p2, return 0; If p1>p2, Returns a positive value ; If p1<p2, Returns a negative value ;

③strcat(p1, p2)------ take p2 Attach to p1 after , return p1;

④strcpy(p1, p2)------ take p2 Copy to p1, return p1.

3.3.3 Arrays and pointers

arr[j] == *(&arr[0]+j) == *(arr+j) == *(j+arr) == j[arr]