recursive

Function recursion is the function calling itself , To set exit conditions , Otherwise, it will run until the memory space is exhausted

The application of recursion 1

Hanoi

Stick it for a while python Written Hanoi Tower code , The mind is the same , Smart you will definitely write him C Language code , So I won't post code .
Hanoi Tower code implementation

The application of recursion 2

Quick sort
The basic idea ： Divide and rule
Find a benchmark value （ Just order one , Habit is the number in the middle of the array ）, Find the number larger than the reference point from left to right (i It's a subscript ) And looking for a number smaller than the reference point from right to left （j It's a subscript ）, Then exchange the two numbers , When i exceed j To exit the loop , At this point, the array is divided into two segments , The left is smaller than the right , Then recurse the arrays at both ends until each array has only one element .
Test code ：

void quick_sort(int array[],int left,int right);

void quick_sort(int array[],int left,int right)
{
    
    int i = left,j = right;// Traversal array 
    int temp;// The cornerstone of exchange 
    int qovit;// Selected reference value 
    qovit = array[(left + right)/2];
    while(i<=j)// Go through the array 
    {
    
        while(array[i]<qovit)// Select the number on the left that is greater than the reference value to jump out of the loop 
        {
    
            i++;
        }
        while(array[j]>qovit)// Select the number on the right that is greater than the reference value to jump out of the cycle 
        {
    
            j--;
        }
        if(i<j)// Exchange the two numbers selected above 
        {
    
            temp = array[i];
            array[i] = array[j];
            array[j] = temp;
            i++;// Note here that the value of the indicator should be changed after the exchange , Otherwise, there is no circulation , Don't ask me how I know 
            j--;
        }
    }
    if(left<j)
    {
    
        quick_sort(array,left,j);// Call quick sort recursively on the left 
    }
    if(i<right)
    {
    
        quick_sort(array,i,right);// Call quick sort recursively on the right 
    }
}

int main(void)
{
    
    int array[]={
    111, 21, 32, 55, 2, 543, 520, 11, 23, 88};
    int length = sizeof(array) / sizeof(array[0]);
    quick_sort(array,0,length-1);
    printf(" The result of sorting is ：");
    for(int i=0;i < length;i++)
    {
    
        printf("%d ",array[i]);
    }
    return 0;
}

result ：