VBA如何使用字符串变量循环instr函数？

I just started learning VBA and I am trying to get an if and loop function to work together. I basically want to search for @ in column A and if there is @ then = ok, if not= "not valid". I get it to work for one row but to loop it for an entire column. Please kindly advise. ps. please be indulgent with my ugly first timer code.I just started learning VBA and I am trying to