The scanf and printf functions are part of stdio.h. Use scanf for input, and printf to print. The %d constructs in the print strings convert variables from the list, in the same order. The letter gives the type. The %d reads or prints a decimal integer, while the %f converts a floating point value.

Notice that, for input, the variables are given with an ampersand: as &n1 instead of just the n1 needed to print. We're not ready to explain this. For now, just note that it allows the function to set the value of the variable; without, the function can only read it.