triangle.cpp: In function 'int main()':
triangle.cpp:11:10: 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:12:10: 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);
~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~