Compilare: user.c: In function ‘main’: user.c:19:5: warning: implicit declaration of function ‘strlen’ [-Wimplicit-function-declaration] freopen("swap.in","r",stdin),freopen("swap.out","w",stdout),gets(s),gets(t),n=strlen(s); ^ user.c:19:83: warning: incompatible implicit declaration of built-in function ‘strlen’ [enabled by default] freopen("swap.in","r",stdin),freopen("swap.out","w",stdout),gets(s),gets(t),n=strlen(s); ^ user.c:19:12: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("swap.in","r",stdin),freopen("swap.out","w",stdout),gets(s),gets(t),n=strlen(s); ^ user.c:19:41: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen("swap.in","r",stdin),freopen("swap.out","w",stdout),gets(s),gets(t),n=strlen(s); ^ user.c:19:69: warning: ignoring return value of ‘gets’, declared with attribute warn_unused_result [-Wunused-result] freopen("swap.in","r",stdin),freopen("swap.out","w",stdout),gets(s),gets(t),n=strlen(s); ^ user.c:19:77: warning: ignoring return value of ‘gets’, declared with attribute warn_unused_result [-Wunused-result] freopen("swap.in","r",stdin),freopen("swap.out","w",stdout),gets(s),gets(t),n=strlen(s); ^ /tmp/ccnOoFJN.o: In function `main': user.c:(.text.startup+0x5b): warning: the `gets' function is dangerous and should not be used.