For specifying the number of digits, tipically we use the command round, for example:

round(pi, digits=2)

[1] 3.14

However, we can also use sprintf  command to deal with both the number of digits and the + or – in your equation, for example:

sprinf(“%3.2f”,pi)

[1] “3.14”

Note that, 3.2f controls the number of digits and the symbol % forces the + or – sign in a equation.