Compilare: user.cpp: In function ‘std::__cxx11::string reversepolishnotation(std::__cxx11::string)’: user.cpp:37:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0;i< exp.size();i++) ~^~~~~~~~~~~~ user.cpp: In function ‘int value(char, int*)’: user.cpp:90:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<exp.size();i++) ~^~~~~~~~~~~ user.cpp: In function ‘int valuefunction()’: user.cpp:124:9: warning: this ‘if’ clause does not guard... [-Wmisleading-indentation] if(isdigit(exp[it])) ^~ user.cpp:126:13: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the ‘if’ it++; ^~ user.cpp: In function ‘int main()’: user.cpp:141:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=2;i<s.size();i++) ~^~~~~~~~~ user.cpp:148:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s.size();i++) ~^~~~~~~~~ user.cpp: In function ‘int val(int, int, char)’: user.cpp:84:1: warning: control reaches end of non-void function [-Wreturn-type] } ^