变量使用需要先声明数据类型变量分为全局变量与局部变量全局变量整个程序全局调用，局部变量只对当前函数有效全局变量整个程序全局调用，局部变量只对当前函数有效，例如这里声明了两个同名变量item
其中主循环loop里声明的是局部变量，同名局部变量会覆盖全局变量Serial115200global_variateitemint123Serialprintlnitemitem888Serialprintlnitemlocal_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