petrol.cpp: In function 'int main()': petrol.cpp:10: warning: unused variable 'a' petrol.cpp:10: warning: unused variable 'b' petrol.cpp:12: warning: ignoring return value of 'int fscanf(FILE*, const char*, ...)', declared with attribute warn_unused_result petrol.cpp:15: warning: ignoring return value of 'int fscanf(FILE*, const char*, ...)', declared with attribute warn_unused_result petrol.cpp:29: warning: ignoring return value of 'int fscanf(FILE*, const char*, ...)', declared with attribute warn_unused_result