long s; if( (n==1)||(n==2)) s=2; else s=n+fun(n-1); return(s); } main( ) {long x; x=fun(4);接上题printf("%ld\n",x)

long s; if( (n==1)||(n==2)) s=2; else s=n+fun(n-1); return(s); } main( ) {long x; x=fun(4);接上题printf("%ld\n",x)
long s; if( (n==1)||(n==2)) s=2; else s=n+fun(n-1); return(s); } main( ) {long x; x=fun(4);
接上题printf("%ld\n",x)

long s; if( (n==1)||(n==2)) s=2; else s=n+fun(n-1); return(s); } main( ) {long x; x=fun(4);接上题printf("%ld\n",x)
fun(4)=4+fun(3)
=4+3+fun(2)
=7+fun(2)
=7+2
=9