Compilare: user.cpp: In function ‘void infix_postfix(char*)’: user.cpp:35:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<strlen(exp);i++) ^ user.cpp:40:52: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(exp[i]>='0' and exp[i]<='9' and i<=strlen(exp)) ^ user.cpp: In function ‘void evaluation()’: user.cpp:85:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<strlen(res);i++) ^