foo.cpp: In function 'int msum(int, int)':
foo.cpp:7:23: error: 'stdin' was not declared in this scope
 freopen("mine.in","r",stdin);    
                       ^
foo.cpp:7:28: error: 'freopen' was not declared in this scope
 freopen("mine.in","r",stdin);    
                            ^
foo.cpp:8:24: error: 'stdout' was not declared in this scope
 freopen("mine.out","w",stdout); 
                        ^
foo.cpp: In function 'int main()':
foo.cpp:35:14: error: 'stdin' was not declared in this scope
       fclose(stdin);fclose(stdout); 
              ^
foo.cpp:35:19: error: 'fclose' was not declared in this scope
       fclose(stdin);fclose(stdout); 
                   ^
foo.cpp:35:28: error: 'stdout' was not declared in this scope
       fclose(stdin);fclose(stdout); 
                            ^
foo.cpp:21:10: warning: unused variable 'd' [-Wunused-variable]
 {int b,c,d,e,f,g;
          ^
foo.cpp:21:12: warning: unused variable 'e' [-Wunused-variable]
 {int b,c,d,e,f,g;
            ^
foo.cpp:21:14: warning: unused variable 'f' [-Wunused-variable]
 {int b,c,d,e,f,g;
              ^
foo.cpp:21:16: warning: unused variable 'g' [-Wunused-variable]
 {int b,c,d,e,f,g;
                ^