Compilare: main.cpp: In function 'int main()': main.cpp:5:39: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("submultimi.in","r",stdin); ^ main.cpp:6:41: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("submultimi.out","w",stdout); ^ main.cpp:9:28: warning: iteration 19 invokes undefined behavior [-Waggressive-loop-optimizations] for(i=1;i<=20;i++) x[i]=i; ~~~~^~ main.cpp:9:14: note: within this loop for(i=1;i<=20;i++) x[i]=i; ~^~~~