Compilare: user.c: In function ‘main’: user.c:6:30: warning: passing argument 3 of ‘freopen’ from incompatible pointer type [-Wincompatible-pointer-types] freopen("adunare.in","r","stdin"); ^~~~~~~ In file included from user.c:1:0: /usr/include/stdio.h:278:14: note: expected ‘FILE * restrict {aka struct _IO_FILE * restrict}’ but argument is of type ‘char *’ extern FILE *freopen (const char *__restrict __filename, ^~~~~~~ user.c:7:31: warning: passing argument 3 of ‘freopen’ from incompatible pointer type [-Wincompatible-pointer-types] freopen("adunare.out","w","stdout"); ^~~~~~~~ In file included from user.c:1:0: /usr/include/stdio.h:278:14: note: expected ‘FILE * restrict {aka struct _IO_FILE * restrict}’ but argument is of type ‘char *’ extern FILE *freopen (const char *__restrict __filename, ^~~~~~~ user.c:6:5: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("adunare.in","r","stdin"); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ user.c:7:5: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("adunare.out","w","stdout"); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ user.c:9:5: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d",&a,&b); ^~~~~~~~~~~~~~~~~~~