Compilare: user.c: In function ‘main’: user.c:27:5: warning: implicit declaration of function ‘isalpha’ [-Wimplicit-function-declaration] if(!(isalpha(ch)) && isalpha(p1)){ ^ user.c:8:14: warning: unused variable ‘p2’ [-Wunused-variable] char ch, p1, p2, back1, back2; ^ user.c:6:15: warning: variable ‘file2’ set but not used [-Wunused-but-set-variable] FILE *file1, *file2; ^ user.c:23:6: warning: ignoring return value of ‘fopen’, declared with attribute warn_unused_result [-Wunused-result] fopen("nc.in", "r"); ^ user.c:30:20: warning: ‘p1’ may be used uninitialized in this function [-Wmaybe-uninitialized] if((ch=='.'&&p1!='.') || ch=='!' || ch=='?' || (ch=='.'&&back1=='.'&&back2=='.')){ ^ user.c:15:75: warning: ‘back2’ may be used uninitialized in this function [-Wmaybe-uninitialized] if((ch=='.'&&back1!='.') || ch=='!' || ch=='?' || (ch=='.'&&back1=='.'&&back2=='.')){ ^ user.c:15:70: warning: ‘back1’ may be used uninitialized in this function [-Wmaybe-uninitialized] if((ch=='.'&&back1!='.') || ch=='!' || ch=='?' || (ch=='.'&&back1=='.'&&back2=='.')){ ^