Compilare: main.cpp: In function 'int main()': main.cpp:61:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int len = 1; len <= input.size(); len++) ~~~~^~~~~~~~~~~~~~~ main.cpp:69:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = len; i < input.size(); i++) ~~^~~~~~~~~~~~~~ main.cpp: In function 'int toNumber(char)': main.cpp:26:1: warning: control reaches end of non-void function [-Wreturn-type] } ^ main.cpp: In function 'int main()': main.cpp:47:34: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("strdup.in", "r", stdin); ^ main.cpp:48:36: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("strdup.out", "w", stdout); ^