/in/foo.c:2:12: error: unknown type name 'a'
 void msort(a[],n){
            ^
/in/foo.c:2:16: error: unknown type name 'n'
 void msort(a[],n){
                ^
/in/foo.c: In function 'main':
/in/foo.c:20:2: warning: implicit declaration of function 'msort' [-Wimplicit-function-declaration]
  msort(a,n);
  ^~~~~