foo.cc: In function 'int main()':
foo.cc:10:8: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
 freopen("1243.in","r",stdin);freopen("1243.out","w",stdout);
 ~~~~~~~^~~~~~~~~~~~~~~~~~~~~
foo.cc:10:37: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
 freopen("1243.in","r",stdin);freopen("1243.out","w",stdout);
                              ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
foo.cc:11:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
 scanf("%d%d%d%d",&m,&n,&cost,&L);
 ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.cc:13:45: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
 for(int j=1;j<=m;j++) scanf("%d",&sum[i][j]),sum[i][j]+=sum[i][j-1];
                       ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。