Question

I am trying to read from the command line either a non negative number or a minus sign and if the input is not one of those the program terminates so I did the following:

while((scanf("%d", &n)==1 && n>-1 && (input=1)) || (scanf("%c", &delete)==1 && delete=='-' && (input=2)))

input is an integer and indicates which was read a number or the minus sign (input=1 & input=2 in the loop are intended).

Now, the program works for the numbers, but if I enter a minus sign the first scanf() reads it but doesn’t put it back apparantly, so the second scanf() finds nothing and terminates the program.

However, if I enter -- (two minus signs) the first scanf() reads one and the second scanf() reads the other and it all works correctly.

The input from the command line can’t be changed, it has to be one minus sign. What is the best way of solving this?

Note that I do know how to use getchar() to read the input and then check it but I don’t want to do that its a hassle.

Answer 1

The best way is to read entire lines of text into a buffer, and then inspect the contents of the buffer, not relying on brittle chains of reading which depend on pushback.

Just use fgets() and sscanf().