Main.cc: In function ‘int main()’: Main.cc:11:2: error: ‘strlwr’ was not declared in this scope strlwr(a);//大写变小写 strupr 小写变大写 ^~~~~~ Main.cc:11:2: note: suggested alternative: ‘strstr’ strlwr(a);//大写变小写 strupr 小写变大写 ^~~~~~ strstr