Using recursive functions to solve the inverse problem of strings

One 、 Overview of recursive functions

         In the process of programming with process oriented programming language , Generally, it is based on structured programming ideas 、 Modular programming method to write programs and organize code . Familiar to us C Language is such a kind of programming language , It usually carries out the modular organization of the program in the unit of function ,C The source program is composed of a main function and several non main functions . The computer is executing C The program , Is in order from the main function main() Start execution , If you call other functions , Then the main function pauses execution , Instead, execute the corresponding function , After the function is executed , Return the main function , Main function continues to execute , This is called function call . Not only the main function can call other functions , Various functions can also be called each other , If a function calls itself , We call it recursive call of function . In the solution of some special problems , Using recursive functions can sometimes be very efficient .（ Hanoi The problem is also a typical application of recursive algorithm ）( Better reading experience , Please visit Programmers are on the road )
         recursive （Recursion） In computer science, it refers to a method to solve a problem by repeatedly decomposing a problem into a similar subproblem , Its core idea is the strategy of divide and rule . Recursive algorithm is suitable for solving the following three kinds of problems ：

1. Data is defined recursively . Such as Fibonacci function .
2. The solution of the problem is implemented by recursive algorithm . Such as Hanoi problem .
3. The structural form of data is defined recursively . Two fork tree 、 Generalized table, etc .

Two 、 String inverse example solution

2.1 Title Description

         Write a function to reverse the string （ Such as a string "abcde" become "edcba"）.

2.2 Analysis and solution

         Reverse the string , You can swap the first string with the last string , Then reverse the rest of the string , The length of the remaining string is subtracted from the original length 2, In order to reduce the scale , The rest of the string inversion method is the same as the first time , If the string length ≤1, Then the recursive condition ends . The procedure is as follows ：

#include<stdio.h>
//start,end Subscript for the beginning and end of the string 
void convert_str(char *str, int start, int end){
    
	char ch;
	if((end - start) < 1){
      // <1 Description string   There is only one character , No need to exchange , Recursion end condition 
		return ;  
	}else{
    
	
		ch = str[start];
		str[start] = str[end];
		str[end] = ch;
        convert_str(str,start+1,end-1); // Call this function recursively , Swap the remaining strings 
	}
}
int main(){
    

		char x[] = "abcdefgh";
		convert_str(x,0,7);

		printf(" The inverse of the string is : %s \n", x);

		return 0;
}

3、 ... and 、 summary

        1） The essence of recursion is how to transform large-scale 、 The more difficult problems become smaller 、 Easy to solve the same problem , Smaller problems become smaller problems , And to a certain extent, its solution can be obtained directly , So we can get the solution of the original problem . Besides , Also pay attention to the termination conditions of recursion , Which is the exit of recursion , If the export conditions are set incorrectly , The program cannot be terminated , This will cause the program to crash .
        2） The implementation of recursion benefits from the data structure of stack , Every call to the function , Stack will be used to save function parameters 、 local variable 、 Return address and other data , therefore , When using recursion , We must consider the depth of recursion , If it's too deep , It is easy to cause stack overflow , Cause problem solving failure .