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:25:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(s[i]==')'&&i<strlen(s)) {nrd--; i++; if(i==strlen(s)-1) nrd=0;} ^ user.cpp:25:72: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(s[i]==')'&&i<strlen(s)) {nrd--; i++; if(i==strlen(s)-1) nrd=0;} ^ user.cpp:27:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(nrd==0&&i<strlen(s)-1) ^ user.cpp:32:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i<strlen(s)) ^ user.cpp:38:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(s[i]!='('&&i<strlen(s)) ^ user.cpp: In function ‘int main()’: user.cpp:52:17: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] s[strlen(s)]=NULL; ^