prefix.cpp: In function 'int main()': prefix.cpp:16: warning: format '%s' expects type 'char*', but argument 2 has type 'char (*)[21]' prefix.cpp:11: warning: unused variable 'nr' prefix.cpp:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result prefix.cpp:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result prefix.cpp:13: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result prefix.cpp:15: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result prefix.cpp:16: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result prefix.cpp:19: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result prefix.cpp:20: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result prefix.cpp:31: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result