& and no &

[ncode]

I dont know why. sometime, when performing scanf it require & while sometime(in string), it dont.

printf("%d",&num1); <---------------no string

printf("%s",num1); <----------------string

ty.

[iceaway]

You should (almost) never use & with printf, as it takes the value of its arguments, not a pointer (except when using strings...). You should (almost) always use & with scanf as it need to write to the arguments passed to the function.

[ncode]

You should (almost) never use & with printf, as it takes the value of its arguments, not a pointer (except when using strings...). You should (almost) always use & with scanf as it need to write to the arguments passed to the function.

NONNO. I mistype. It should be scanf!

[CommonTater]

NONNO. I mistype. It should be scanf!

You need the & with ints and floats etc. because these are values and you need to hand it an address.
You don't need it with arrays and strings because C treats these as pointers to begin with.