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Lỗi biên dịch:

Main.cc: In function ‘void dosth(char*)’:
Main.cc:8:9: error: ‘lstrim’ was not declared in this scope
     a = lstrim(a);
         ^~~~~~
Main.cc:8:9: note: suggested alternative: ‘stdin’
     a = lstrim(a);
         ^~~~~~
         stdin
Main.cc:9:9: error: ‘rstrim’ was not declared in this scope
     a = rstrim(a);
         ^~~~~~
Main.cc:9:9: note: suggested alternative: ‘stdin’
     a = rstrim(a);
         ^~~~~~
         stdin
Main.cc:10:9: error: ‘strlower’ was not declared in this scope
     a = strlower(a);
         ^~~~~~~~
Main.cc:10:9: note: suggested alternative: ‘strtok_r’
     a = strlower(a);
         ^~~~~~~~
         strtok_r
Main.cc:11:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 1; i < strlen(a); i++)
                     ~~^~~~~~~~~~~
Main.cc:13:20: error: ‘toupper’ was not declared in this scope
             a[i] = toupper(a[i]);
                    ^~~~~~~
Main.cc: In function ‘int main()’:
Main.cc:19:18: warning: format ‘%d’ expects argument of type ‘int*’, but argument 2 has type ‘int’ [-Wformat=]
     scanf("%d", n);
                  ^
Main.cc:22:15: warning: ‘char* gets(char*)’ is deprecated [-Wdeprecated-declarations]
         gets(a);
               ^
In file included from /usr/include/stdio.h:862:0,
                 from Main.cc:1:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:232:1: note: declared here
 gets (char *__str)
 ^~~~
Main.cc:19:10: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", n);
     ~~~~~^~~~~~~~~
Main.cc:22:13: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result]
         gets(a);
         ~~~~^~~