Use unsigned variables : Data Type « Data Type « C Tutorial

When declaring a numeric variable in C, you can use 'signed' or 'unsigned'.

Variable is signed unless you specifically type unsigned before the variable type:

1. The standard int variable can hold values from -32,768 up to 32,767.
2. That's half negative numbers, from -32,786 to -1, and then half positive numbers, from 0 up to 32,767.
3. An unsigned number means that the variable holds only positive values.
4. Your typical unsigned int has a range from 0 to 65,535.