The way I'd do it is with a simple function: pass it the two guesses and it returns a string.
Inside the function, I'd use a 2D array of char pointers, and use the inputs as the two indexes. the string is the result. Convert 'S', 'R', and 'P' to 0, 1, and 2 then just use those to index the array.
No
if
is needed!
In fact, I'd expand it slightly to have four index values: Stone, Rock, Paper and "other" with "other" returning a "unknown input" message. Again, an array would be a simple way to check and convert the inputs:
int InputToIndex(char c)
{
static const char inputs[3] = "SRP";
int i;
for (i = 0; i < sizeof(inputs); i++)
{
if (inputs[i] == c) break;
}
return i;
}