foo.cc: In function 'int get_max_len(int, int)':
foo.cc:30:6: warning: unused variable 'sum' [-Wunused-variable]
int sum;
^~~
foo.cc: In function 'void readfile()':
foo.cc:22:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
scanf("%d%d",&n,&m);
~~~~~^~~~~~~~~~~~~~
foo.cc:25:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
scanf("%d",&num[i][j]);
~~~~~^~~~~~~~~~~~~~~~~