triangle.cpp: In function 'int main()':
triangle.cpp:16:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
freopen("input.in", "r", stdin);
~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
triangle.cpp:17:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
freopen("output.out", "w", stdout);
~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~