Binary tree sorting (C language, char type)

#define _CRT_SECURE_NO_WARNINGS   // Binary tree sorting （char type ）
#include<stdio.h>                 // Array index from 1 Start 
#include <string.h>

void move_char(char a[]) {      // Will array a Move the whole backward by one bit , Give Way a[0] invalid 
	for (int i = strlen(a); i > 0; i--) {
		a[i] = a[i - 1];
	}
}

void exch_char(char a[], int i, int j) {	// In exchange for a[i] and a[j] Value 
	char temp;
	temp = a[i];
	a[i] = a[j];
	a[j] = temp;
}

void swim_char(char a[], int k) {	// Floating up k The element of location   To the right place （ The tree is descending from top to bottom ）
	while (k > 1 && a[k / 2] < a[k]) {
		exch_char(a, k / 2, k);
		k = k / 2;
	}
}

void sink_char(char a[], int k, int a_length) {	// Sinking k Location elements , Give priority to exchanging positions with the largest left and right children （ The tree is descending from top to bottom ）
	while (2 * k <= a_length) {                 //a_length Is an array a Remove a[0] The length after 
		int j = 2 * k;
		if (j < a_length && a[j] < a[j + 1]) j++;
		if (!(a[k] < a[j])) break;
		exch_char(a, k, j);
		k = j;
	}
}

void BiTree_sort_char(char a[]) {	// Binary tree sorting ,a_length Is an array a Remove a[0] The length after 
	int a_length = strlen(a) - 1;
	for (int k = a_length / 2; k >= 1; k--) {	// Make the binary tree orderly （ Descending from top to bottom ）
		sink_char(a, k, a_length);
	}

	while (a_length > 1) {		// Sort ascending from top to bottom 
		exch_char(a, 1, a_length--);
		sink_char(a, 1, a_length);
	}
}

int main() {
	char a[100] = {};

	printf(" Please enter the string to sort ：\n");
	scanf("%s", a);
	move_char(a);                //a[0] no need 

	BiTree_sort_char(a);

	printf("\n The result after ascending is ：\n");
	for (int i = 1; i <= strlen(a); i++) {
		printf("%c ", a[i]);
	}
	printf("\n");
	return 0;
}

test result ：