submatrix1.cpp: In function 'void read()': submatrix1.cpp:35: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result submatrix1.cpp:41: warning: ignoring return value of 'char* fgets(char*, int, FILE*)', declared with attribute warn_unused_result submatrix1.cpp: In function 'int main()': submatrix1.cpp:341: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result submatrix1.cpp:343: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result In file included from /usr/include/stdio.h:910, from submatrix1.cpp:1: In function 'char* fgets(char*, int, FILE*)', inlined from 'void read()' at submatrix1.cpp:41: /usr/include/bits/stdio2.h:253: warning: call to '__fgets_chk_warn' declared with attribute warning: fgets called with bigger size than length of destination buffer