c語言關鍵字const_C ++ const關鍵字| 查找輸出程序| 套裝1

c語言關鍵字const

Program 1:

程序1：

#include <iostream>
using namespace std;
void fun(int& A) const
{
A = 10;
}
int main()
{
int X = 0;
fun(X);
cout << X;
return 0;
}

Output:

輸出：

[Error] non-member function 'void fun(int)' cannot have const qualifier.

Explanation:

說明：

The above code will generate an error because we cannot define, the non-member function as a const. Without a const keyword the above code will work fine.

上面的代碼將產生錯誤，因為我們無法將非成員函數定義為const 。如果沒有const關鍵字，則上面的代碼可以正常工作。

Program 2:

程式2：

#include <iostream>
using namespace std;
int main()
{
const int X = 0;
int* ptr;
ptr = &X;
*ptr = 10;
cout << X;
return 0;
}

Output:

輸出：

error: invalid conversion from ‘const int*’ to ‘int*’ [-fpermissive] ptr = &X;

Explanation:

說明：

The above program will generate an error in C++, C++ does not allow modification in a constant using pointer, but we can modify the value of a constant in C language. The below program in C language will work fine.

上面的程序在C ++中會產生錯誤，C ++不允許使用指針修改常量，但是我們可以在C語言中修改常量的值。下面的C語言程序可以正常運行。

#include <stdio.h>
int main()
{
const int X = 0;
int* ptr;
ptr = &X;
*ptr = 10;
printf("%d", X);
return 0;
}

Program may run on C language compiler, but it is not a standard that we can change the constant. In C language compiler – it can be changed through the pointer.

程序可以在C語言編譯器上運行，但是我們不能更改常量不是標準。在C語言編譯器中–可以通過指針進行更改。

Program 3:

程式3：

#include <iostream>
using namespace std;
class Sample {
const int A;
const int B;
public:
Sample(): A(10), B(20)
{
}
void print()
{
cout << A << " " << B;
}
};
int main()
{
Sample S;
S.print();
return 0;
}

Output:

輸出：

10 20

Explanation:

說明：

The above code will print "10 20" on the console screen.

上面的代碼將在控制臺屏幕上顯示“ 10 20” 。

Let's understand the program step by step.

讓我們逐步了解程序。

Here we created a class Sample that contains two const data members A and B. As we know that we can assign the values of constant at the time of declaration. But here we use the concept of member initialize list.

在這里，我們創建了一個Sample類，其中包含兩個const數據成員A和B。眾所周知，我們可以在聲明時分配常量的值。但是這里我們使用成員初始化列表的概念。

Sample ():A(10),B(20)
{
}

We can assign value to const data members using the member initialize list. We can initialize members by a colon (:) with members and value in the constructor.

我們可以使用成員初始化列表為const數據成員分配值。我們可以初始化一個冒號成員：在構造函數中成員和值()。

Here we also defined a print() member function, which is used to print values of data members.

在這里，我們還定義了一個print()成員函數，該函數用于打印數據成員的值。