原课程链接：C程序设计进阶

const vs. static

const 限制指针实参的功能

指针常量：

  • 不能修改指针所指向的地址。在定义时必须立即初始化。

  • 示例：

    char* const ptr = &some_char; // ptr 是一个指向 char 的常量指针
*ptr = 'a'; // 合法，修改了 ptr 所指向的 char 的值
ptr = &another_char; // 错误，不能修改 ptr 的值

常量指针：

  • 不能修改指针所指向地址的内容，但可以改变指针所指向的地址。

  • 示例：

    const char* ptr; // ptr 是一个指向 char 的常量指针
char const* ptr; // 与上一行等效
*ptr = 'a'; // 错误，不能修改 ptr 所指向的 char 的值
ptr = &another_char; // 合法，可以改变 ptr 的值

static 在函数内部或类中声明的静态变量，其生命周期跨越整个程序执行过程（在循环中多次执行，每次循环的初始值继承了上一次循环的值），且只初始化一次。

string literal

#include <iostream>
using namespace std;

int main()
{
    // input arguments
    int k=0, m=0, n=0;
    cin>>k;
    cin>>m>>" ">>n; // wrong expression.
}

cin operator automatically skips any whitespace, including spaces and newlines. it’s illegal to use “ ” with cin, because it is string literal, cin could not hold string.

**getline(cin, line);**where line is a string. This will read an entire line of input, including spaces, until it encounters a newline

cin.getline(str, 101);

return, break, exit

/* eg: 2.3.4.cpp
2. C程序设计进阶
3. 第三周
3. 编程题＃4：扩号匹配问题
// Recursively find the next pair

void find_pair(char *str){
    int i = 0;
    remove(str);
    char  boy= '(', girl= ')';
    while(str[i] != '\0'){
        if(str[i] == boy){
            int j = i + 1;
            while(str[j] != '\0') { 
                if(str[j] == girl){
                str[i]=' ';
                str[j]=' ';
                find_pair(str); 
                return ;
                }
                // If we find another boy before a girl, break, i++     
                if(str[j] == boy) break; 
                j++;
            }    
        }
        i++;
    }
}

return: In a function, it ends the execution of the function, and returns control to the calling function. It can also return a value to the caller, which can be used in the expression.

break: it is used to terminate the loop or switch statement and transfer execution to the statement immediately following the loop or switch. It doesn’t end the execution of the function.

exit: it terminates the entire program, not just the current function. It’s usually used to end the program immediately in response to some error condition.

Pointers

Array address and pointers

6.2.5 Type 6.3.2.1 Lvalues, array and function designators. 6.5.2.1 Array subscripting

array name represents the address of the first element in array. or array name is the pointer that point to the first element of the array.

// example

int main()
{
	a[5]={10,2,3,4,5};
	cout<< a <<endl;
	cout<< a[0] <<endl;
	cout<< &a[0] <<endl;
	cout<< a* <<endl; 
}

// output
0017F754
10
0017F754
10

a = &a[0]
a[0] = a*

Pointer, calculation order, because pointer and – have the same operation level, from right to left; *p–, equivalent to (*p)–, first take the value of *p, then p-1; *–p, equivalent to *(–p), first p-1, then take the value of *p;

指针，计算顺序，因为指针和 – 运算级别相同，从右至左； *p– ，等同于 (*p)–，先取 *p的值，再 p-1； –p，等同于(–p)， 先p-1，再取 *p的值；

Function declaration

Function declaration must be ahead of main(), the function body could be after main();

function declaration = signature/ prototype = return type, function name, argument lists, eg.

bool checkPrime(int)

return type = bool

function name = checkPrime

argument lists = int

Formal parameter/formal parameter; 形参/ 形式参数；

Actual parameter/actual parameter; 实参/ 实际参数；

arguments pass between global or local.

Variable scope 变量的作用域

Difference compare

Array

#include <iostream>
using namespace std;

void change(int a[])
{
	a[0]=30; a[1]=50;
}

int main()
{
	int a[2]={3,5};
	change(a);
	cout<<a[0]<<””<<a[1]<<endl;

	return 0;
}

**// output value 30 50**

Why function void change() could change the arguments in function main() ?

because main() pass the address of array a to change();

then change () visit the address of array in main(), and change the value of arguments in array.

  • array name is a constant, not a variable, we can not change a, but can change the inside elements of a.

Arguments

#include <iostream>
using namespace std;

void change(int a, int b)
{
	a =30; b=50;
}

int main()
{
int a[2]={3,5};
change(a[0],a[1]);
cout<<a[0]<<””<<a[1]<<endl;

return 0;
}

**// output value 3 5**

Why here is no value change on array, because function main() pass the arguments of array to function change() directly. void type function has no return value, so there is no change to main();

bubble sorting

#include <iostream>
using namespace std;

int order(n,a[])
{
for(int i=0; i<n; i++)
if (a[i]< a[i+1]){
	cout<< a[i]<< endl;}
else {
	cout<< a[i+1]<< endl;}

return 0;

}

int main()
{
int n=0, a[];
cin>> n;
cin>> a[n];
cout<<order(n, a[])<<endl;

return 0;
}

#include <iostream> // bubble sorting algorithm
    using namespace std;

    int main() {
        int n, a[1000]; // n < 1001, a is used to store these numbers
        cin >> n;  
        // input n
        for (int i = 0; i < n; i++) {
          cin >> a[i];
    }  
    // Bubble sort, constantly compare two adjacent numbers, if the order is wrong, then swap
    for (int i = 0; i < n - 1; i++) {
      for (int j = 1; j < n - i; j++) {      
        if (a[j - 1] > a[j]) {
          int temp = a[j];
          a[j] = a[j - 1];
          a[j - 1] = temp;
        }    
      }  
    }  
    // Loop Output
   for (int i = 0; i < n; i++) {
     cout << a[i] << endl;  
   }  
   return 0;
}

the whole process of elements argument shift in the array

Untitled

a[8]a[0]a[1]a[2]a[3]a[4]a[5]a[6]a[7]
i65318724
053167248
131562478
213524678
313245678
412345678

n = 8

j=1, j < 8-i

a[j - 1] > a[j]?

i deal with the outer for loop, output the value on the row above;

j deal with the inner for loop, output the value on the colum above;

Programming Assignment: 综合编程练习（1）

1：寻找下标

#include <iostream>
using namespace std;

int seek(a[])
{
for(int i=0;i<n;i++)
	{
	if(x[i]=i){return i;}
	else {return "N";}
	return 0;
	}
}

int n(n>0, n<100), a[n];
int main()
{
cin>> n;
cin>> a;
seek(a[n]);
cout<<seek(a)<<endl;

return 0;
}

// output value

#include <iostream>
using namespace std;

int seek(int a[], int n)
{
int i;
for(i=0;i<n;i++)
{
if(a[i]==i)
{
return i;
}
}
return -1;
}

int main()
{
int n;
cin >> n;
if(n <= 0 || n >= 100)
{
cout << "Invalid input value for n. Please enter a value between 1 and 99." << endl;
return 0;
}
int a[n];
for(int i=0;i<n;i++)
{
cin >> a[i];
}
int result = seek(a, n);
if(result == -1)
{
cout << "N" << endl;
}
else
{
cout << "a[" << result << "] = " << a[result] << endl;
}
return 0;
}