/in/ex2.c: In function 'main':
/in/ex2.c:7:5: warning: implicit declaration of function 'gets_s' [-Wimplicit-function-declaration]
     gets_s(day,4);
     ^~~~~~
/in/ex2.c:25:9: warning: implicit declaration of function 'printf_s' [-Wimplicit-function-declaration]
         printf_s("%8s",Week[i]);
         ^~~~~~~~
/in/ex2.c:44:5: warning: statement with no effect [-Wunused-value]
     for (i; i< (j + n_day+ 4);i++){
     ^~~
/in/ex2.c:44:19: warning: 'n_day' may be used uninitialized in this function [-Wmaybe-uninitialized]
     for (i; i< (j + n_day+ 4);i++){
                 ~~^~~~~~~
/tmp/ccqYxosx.o: In function `main':
ex2.c:(.text.startup+0x30): undefined reference to `gets_s'
ex2.c:(.text.startup+0xdd): undefined reference to `printf_s'
ex2.c:(.text.startup+0xf6): undefined reference to `printf_s'
collect2: error: ld returned 1 exit status