[C language] use function pointers to make a different calculator

A function pointer

A function pointer is a pointer that stores the address of a function .
Important content of function pointer ：
1. The use of function pointers : Type of function ( The pointer )（ The formal parameter type of the function ）= Function name ; Be careful ： There are variable names that do not need formal parameters of functions ., If a function has no parameters , There is no need to fill in anything ,void Not good either. . After using this , This pointer is a function pointer .
2. Function pointer calls the method of the function :****( The pointer )( Actual parameters ); Be careful ： There are two ways to express the pointer here , For example, it defines a name called *p Function pointer of , The return type of the function is null , No formal parameters . The call here can be written as (*p)(); Or you could write it as p(); These two ways can be written , But for convenience , The first one is not recommended .
3. Function pointers can be used as formal parameters of functions , If you need to pass arguments , You can directly pass the function name .

Realize the idea of calculator program

First of all, calculators should have the most basic operations , That is to say Add, subtract, multiply and divide , Secondly, we should write a simple menu , Then let the user choice , After the selection is Input number Conduct Calculate and print come out , Considering that users may have to Multiple use , So you can add some circular statements , Let users use it many times .
Basically, the problems we need to consider in implementing calculators are all here , In this program , The most important thing is to use array pointers to call the functions of addition, subtraction, multiplication and division , The other parts are simple , Now let's implement this part of the function .

Call the addition, subtraction, multiplication and division function with the function pointer

First look at the code ：

int add(int x, int y)
{
    
	return x + y;
}

int sub(int x, int y)
{
    
	return x - y;
}

int mul(int x,int y)
{
    
	return x * y;
}

int exc(int x, int y)
{
    
	return x / y;
}

void func(int *(pf)(int, int y))
{
    
	int x = 0;
	int y = 0;
	printf(" Please enter two numbers :");
	scanf("%d%d", &x, &y);
	int ret = pf(x, y);
	printf(" The result is :%d\n", ret);
}

stay func In this function , A formal parameter is a function pointer , because The return value of addition, subtraction, multiplication and division , The formal parameters are the same , So just pass different functions in , As mentioned earlier, formal parameters are function pointers that can be directly Pass function name , That's right. func It can realize the operation of the corresponding function and print it out .

Complete code + Run a screenshot

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
void menu() 
{
    
	printf("|-------------------|\n");
	printf("|-------1. Add --------|\n");
	printf("|-------2. reduce --------|\n");
	printf("|-------3. ride --------|\n");
	printf("|-------4. except --------|\n");
	printf("|-------0. sign out ------|\n");
	printf("|-------------------|\n");
}

int add(int x, int y)
{
    
	return x + y;
}

int sub(int x, int y)
{
    
	return x - y;
}

int mul(int x,int y)
{
    
	return x * y;
}

int exc(int x, int y)
{
    
	return x / y;
}

void func(int *(pf)(int, int y))
{
    
	int x = 0;
	int y = 0;
	printf(" Please enter two numbers :");
	scanf("%d%d", &x, &y);
	int ret = pf(x, y);
	printf(" The result is :%d\n", ret);
}
int main()
{
    
	int n = 0;
	int flag = 1;
	while (flag)
	{
    
		menu();
		printf(" Please select the operation you want :");
		scanf("%d", &n);
		switch (n)
		{
    
		case 1:
			func(add);
			break;
		case 2:
			func(sub);
			break;
		case 3:
			func(mul);
			break;
		case 4:
			func(exc);
			break;
		case 0:
			flag = 0;
			break;
		default:
			printf(" Wrong choice , Please reselect !\n");
			break;
		}
	}
	return 0;
}