What is the answer of the program , I got different answers from turbo cpp and dev cpp

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i got different answers from turbo cpp and dev cpp

That is an hint you shouldn't use such a code. For details have a look here: c++ - Undefined behavior and sequence points - Stack Overflow[^].

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What is the answer of the program , I got different answers from turbo cpp and dev cpp

There is no correct answer to this program, or all answers are correct.
It is a gray zone.

S=(R--) + (++R);

The compiler is free to rewrite this code in any way it see fit, no matter the way you read, understand, expect it. So each compiler makes its own truth.
So multiple increment/decrement operations on same variable make the code unpredictable from a compiler to another.
This is 1 of the pitfalls of C language.

because you have written unclear code in

S=(R--) + (++R);

it are 3 statements
1. R--
2. ++R
3. sum up the results of 1. and 2.

So the compiler can decide what to do first. If you left out the braces you get two additional edge cases.

try some clearer code

R--;
S = R;
++R;
S += R

That should result in the same value on all compilers.