submatrix.cpp: In function 'int main()': submatrix.cpp:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result submatrix.cpp:11: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result submatrix.cpp:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result submatrix.cpp:17: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result submatrix.cpp:20: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result submatrix.cpp:12: warning: 'is' may be used uninitialized in this function submatrix.cpp:12: warning: 'ij' may be used uninitialized in this function submatrix.cpp:12: warning: 'js' may be used uninitialized in this function submatrix.cpp:12: warning: 'jj' may be used uninitialized in this function