Compilare: user.cpp: In function ‘void calc(int)’: user.cpp:10:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i<strlen(s)) ^ user.cpp:22:15: warning: suggest explicit braces to avoid ambiguous ‘else’ [-Wparentheses] if(nrd==0) if(s[i]=='/') e=-1; else if(s[i]=='*') e=1; ^ user.cpp:27:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(s[i]!='('&&i<strlen(s)) ^ user.cpp: In function ‘int main()’: user.cpp:41:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<strlen(s);i++) ^