1. The return value of a C++ function cannot be an array, but it can be an integer, floating-point number, pointer, structure or object. You can return an array as part of a structure or object.
2. int arr[];
arr[i]==*(arr+i); &arr[i]==arr+i;
3. Tell the array type and number of elements to the array processing function, and pass them with two different parameters: void fillArray(int arr[], int size);
Do not use void fillArray (int arr[size]);
4. const Size=8;
int sum_arr(int arr[], int n);
void main(){
int cook[Size]={1,2,3,4,5,6,7,8}; cout<<sizeof cook; //The displayed length is 32
int sum=sum_arr(cook,Size);}
int sum_arr( int arr[], int n){
cout<<arr; cout<<sizeof arr; //The length displayed is 4, cook and arr point to the same address,
But sizeof cook is 32 (length of the entire array), sizeof arr is 4 (length of pointer variable)
......
}
5. When protecting the array and making the array as readable data, declare it with const
The function needs to modify the array, the original shape: void f_modify( double arr[], int n);
The function does not modify the array, the original shape: void f_nochange(const double arr[], int n);
8. Use the function of the array interval:
const Size=8;
int sum_arr(const int * begin, const int * end);
void main(){
int cook[Size]={1,2,3,4,5,6,7,8};
int sum=sum_arr(cook, cook+Size); }
int sum_arr(const int * begin, const int * end){
int total=0; const int * pt;
for (pt=begin; pt!=end; pt++)
total=total+ *pt;
}
9. General will refer to pin point to a constant parameter is declared as a pointer to the object can not be used to modify the value of the pointer is pointing, but can modify the position pointer.
int age=39;
const int * pt=&age; //Pointer to a constant object, pointers cannot be used to modify the value of age pointed to, and pt can be made to point to other locations *pt+=1; (illegal)
int * const finger=&age; //The pointer itself is a constant, you cannot modify the position pointed to by the pointer, but you can use finger to modify the value of age
Above finger, *pt are const, *finger and pt are not const.
It is forbidden to assign the address of a constant array to a non-constant pointer, and you can use cast to break this limitation. (P222)
10. Functions and two-dimensional arrays:
int data[3][4]={ {1,2,3,4},{9,2,1,4},{2,4,6,3}}; int total=sum(data,3);
The original form of sum: int sum( int (*arr2)[4], int size); // (*arr2)[4] represents the pointer of an array composed of 4 ints, size represents the number of rows
Or: int sum( int arr2[][4], int size); //These two prototypes arr2 are pointers rather than arrays
(Int *arr2[4] represents an array composed of 4 pointers to int.)
arr2
arr2+r
*(arr2+r)
*(arr2+r)+c
*(*(arr2+r))+c==arr2[r][c]
12.while (*str) 等价于 while (*str!="\0")
#include<iostream>
char * buildstr(char c,int n); //该函数的返回值是一个指针
int main()
{
using namespace std;
char ch;
int times;
cout<<"Enter a character: ";
cin>>ch;
cout<<"Enter an integer: ";
cin>>times;
char * ps=buildstr(ch, times);
cout<<ps<<endl;
delete [] ps; //释放指针所指内存
ps=buildstr('+',20); //释放后可以重新使用指针
cout<<ps<<"Done"<<ps<<endl;
delete [] ps; //释放指针所指内存
return 0;
}
char * buildstr(char c,int n) //该函数的返回值是一个指针
{
char * pt=new char[n+1]; //用new分配动态数组
pt[n]='\0';
while(n-->0)
pt[n]=c;
return pt;
}13. Function and structure: function returns structure
#include "stdafx.h"
#include<iostream>
struct travel_time
{
int hour;
int min;
};
const int mins_perh = 60;
travel_time sum(travel_time t1, travel_time t2);
void showtime(travel_time t);
using namespace std;
int main()
{
travel_time day1 = { 5, 24 };
travel_time day2 = { 6, 48 };
travel_time trip = sum(day1, day2);
cout << "Two days total: ";
showtime(trip);
travel_time day3= {3, 51};
cout << "There days total: ";
showtime(sum(trip, day3));
}
travel_time sum(travel_time t1, travel_time t2) //函数要返回一个travel_time结构，应先声明一个travel_time结构
{
travel_time total;
total.hour = t1.hour + t2.hour + (t1.min + t2.min) / mins_perh;
total.min = (t1.min + t2.min) % mins_perh;
return total;
}
void showtime(travel_time t)
{
cout << t.hour << "hours, " << t.min << "minutes.\n";
}When passing the structure address, it is more convenient for the function not to be defined as the type returned
#include "stdafx.h"
#include<iostream>
#include<cmath>
using namespace std;
struct rect
{
double x;
double y;
};
struct polar
{
double dis;
double angle;
};
void rect_polar(const rect * pxy, polar * pda);
void showploar(const polar * pda);
int main()
{
rect zb;
polar da;
cout << "Enter the x and y value ";
while (cin >> zb.x >> zb.y) //访问结构数据的成员用句点 .
{
rect_polar(&zb, &da); //参数类型是指针，应对结构变量取地址
showploar(&da);
cout << "Next two number(q to quit): ";
}
return 0;
}
void rect_polar(const rect * pxy, polar * pda) //无返回值，用另一个参数来存储所需结果
{
const double rad_to_ang = 57.29577951;
pda->dis = sqrt(pxy->x*pxy->x + pxy->y*pxy->y); //访问结构指针的成员用->
pda->angle = atan2(pxy->y, pxy->x)*rad_to_ang;
}
void showploar(const polar * pda)
{
cout <<"distance="<< pda->dis << ", angle=" << pda->angle;
}14. Declare the string array: string list[5];
写入string数组：for(int i=0;i<5;i++) getline( cin, list[i] );
15. Function recursion (P239 example 7.16)
16. A function think(), the name of the function think is the address of the function think()
Get the function address: process(think); //Transmit the address of the think() function to process()
thought(think()); //Transfer the return value of the think() function to thought()
Declare function pointer: double pam( int ); double (*pf) (int ); pf=pam // pf is a pointer to a function
double *pf (int) ;//Indicates that pf() returns a pointer function
Call a function with a pointer: double x=pam(4); double y=(*pf) (5); or double y=pf (5);
17. The parameter list const double ar[] in the function prototype has the same meaning as const double *ar.
Automatic type judgment auto can only be used for simple single initialization, not for initialization lists.
(1) Function prototype:
const double * f1(const double ar[], int n);
const double * f2(const double [], int );
const double * f3(const double *, int );
(2) Declare pointers to functions:
const double * (*pa) (const double *, int )=f1; //Declare a pointer to f1:
const double * (*pb[3]) (const double *, int )={ f1,f2,f3 }; // Declare a pointer number, point to f1, f2, f3, and initialize:
pb is an array containing 3 pointers, each pointer points to a function, const double *, int as parameters, and returns a const double *.
auto pa=pb; //legal
(3) Function call:
const double *px=pb[0] (av,3); //av,3 is the parameter Get the returned value: double x=*pb[0] (av,3);
const double *py= (*pb[0]) (av,3); Get the returned value: double y=*(*pb[0]) (av,3);
18. Create a pointer to the entire pointer array (P246 Example 7.19)