Compilare: user.c: In function ‘main’: user.c:15:16: warning: implicit declaration of function ‘strlen’ [-Wimplicit-function-declaration] int h1=strlen(a), h2=strlen(b),h3=strlen(c); ^~~~~~ user.c:15:16: warning: incompatible implicit declaration of built-in function ‘strlen’ user.c:15:16: note: include ‘<string.h>’ or provide a declaration of ‘strlen’ user.c:7:35: warning: unused variable ‘d’ [-Wunused-variable] char a[301], b[301], c[301], *d; ^ user.c:8:5: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] (void)freopen("entropy.in","rt",stdin); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ user.c:9:5: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result] (void)scanf("%d\n",&n); ^~~~~~~~~~~~~~~~~~~~~~ user.c:10:5: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] (void)freopen("entropy.out","wt",stdout); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ user.c:12:9: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result] scanf("%[^\n]\n%[^\n]\n%[^\n]\n",a,b,c); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~