Compilare: user.cpp: In function ‘void calc()’: user.cpp:10:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i<strlen(s)) ^ user.cpp:14:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(nrd!=0&&i<strlen(s)) ^ user.cpp:16:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(s[i]!=')'&&i<strlen(s)) ^ user.cpp:26:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(s[i]==')'&&i<strlen(s)) {nrd--; i++;} ^ user.cpp:27:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i==strlen(s)-1) nrd=0; ^ user.cpp:29:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(nrd>=0&&i<strlen(s)-1) ^ user.cpp:34:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i<strlen(s)) ^ user.cpp:40:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(s[i]!='('&&i<strlen(s)) ^ user.cpp: In function ‘int main()’: user.cpp:54:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<strlen(s);i++) if(s[i]>='a'&&s[i]<='z') b[s[i]-'a'+1]=1; ^ user.cpp:55:17: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] s[strlen(s)]=NULL; ^