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),fgets(s,50001,stdin),fgets(t,50001,stdin),n=strlen(s); ^ user.c:19:109: warning: incompatible implicit declaration of built-in function ‘strlen’ [enabled by default] freopen("swap.in","r",stdin),freopen("swap.out","w",stdout),fgets(s,50001,stdin),fgets(t,50001,stdin),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),fgets(s,50001,stdin),fgets(t,50001,stdin),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),fgets(s,50001,stdin),fgets(t,50001,stdin),n=strlen(s); ^ user.c:19:70: warning: ignoring return value of ‘fgets’, declared with attribute warn_unused_result [-Wunused-result] freopen("swap.in","r",stdin),freopen("swap.out","w",stdout),fgets(s,50001,stdin),fgets(t,50001,stdin),n=strlen(s); ^ user.c:19:91: warning: ignoring return value of ‘fgets’, declared with attribute warn_unused_result [-Wunused-result] freopen("swap.in","r",stdin),freopen("swap.out","w",stdout),fgets(s,50001,stdin),fgets(t,50001,stdin),n=strlen(s); ^