foo.cc: In function 'int main()':
foo.cc:5:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
5 | freopen("data.txt","r",stdin);
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
foo.cc:6:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
6 | freopen("ans.txt","w",stdout);
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
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