如何使用递归函数使用4个字符生成m长度字符串数组

Using c++ on visual studio I want a function that generates a string array, assuming that each string in this array has the length m, and the letters to be used in the string production are A, C, G, T. For example If m = 4, then the array should contain 4^4 items "64" just like {AAAA, AAAC, AAAG, AAAT, AACA, AAGA,AATA, ............., TTTA, TTTC,TTTG,TTTT} I manged to get such array using nested for loops but I can not change m with nested for loops:Using c++ on visual studio I want a function th