The cd command in the shell script does not work

Recently I was learning shell scripts and wrote a simple demo. What I want to achieve is to cd a folder and then create files, but when I execute the shell script, I find that the cd command does not take effect. My folders and files are not created

# !/bin/bash
read -p "请输入文件夹的名字:" dirName
if [ -e $dirName ];then
    echo "$dirName 是存在的即将进入文件夹"
    cd $dirNamem
    echo "即将创建文件名为test"
    touch test.c
else
   echo "该文件夹不存在，即将创建文件夹"
   mkdir $dirName
   echo "即将进入$dirName 文件夹中"
   cd $dirName

I checked the information and found that this is because when the shell executes the script, it creates a subshell and executes the commands in the script one by one in the subshell; while the subshell inherits the environment variables from the parent shell, but executes Will not change the environment variables of the parent shell.
I used two methods to make my cd take effect.

1. Use the source command
   When executing a shell script, do not use ./XXX.sh. Instead, use the source xxx.sh method, this will create a file, but directly return to the ~ directory (does not solve the cd not)
2. Adding
   the command exec /bin/bash after cd means that the bash script runs on its current environment or its child environment, but not on its parent environment