#include<stdio.h>
char* my_atoi(int num, char* str) {
    int i = 0; 
 
    do {
        int rem = num % 10;
        str[i++] = rem + '0'; // 直接将余数转换为字符'0'到'9'  
    } while (num /= 10);
     // 直接将余数转换为字符'0'到'9'  
   

    str[i] = '\0'; // 添加字符串结束符 

     return str;
}
int main() {
    int a = 123;
    char arr[4] = { 0 };
    printf("%s", my_atoi(a, arr));
}