Compilare: user.c: In function ‘main’: user.c:7:5: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("cmmdc.in","r",stdin); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~ user.c:8:5: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("cmmdc.out","w",stdout); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ user.c:10:5: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d",&a,&b); ^~~~~~~~~~~~~~~~~~~ user.c:13:11: warning: ‘c’ may be used uninitialized in this function [-Wmaybe-uninitialized] a = c; ~~^~~