Hello,
I'm having trouble with a very simple program. I want it to approximate a square root of a number R. So here is my program :

For example, if you enter R as 3, a as 1, b as 2 and Tol as 0.001, it should return " d " as the square root of we were looking for, "i" as the number of steps to reach it, and "f(d)" as the real value of the function f (obviously close to Tol). But it doesn't work. I've tried to find an error, but I don't see any. Maybe there is a problem in the function f.... but I'm not sure.
I'd be grateful if you could run the program to see what happens, or if you any error. Thanks a lot.

I just tried "Write(*,*)i,d,a,b,f(d)", in one example a wasn't changing and b got b^2, b^4, etc. In another example I got about 3000 iterations were a and b didn't change, and so did d. And I always considered a small interval containing the root. I still don't see the error. Now I guess it's in the do while.

By declaring R in your function, you have set up a new variable R that is specific to that function, and therefore you have made the function unable to access the R in the main program.

If you don't declare it in the function I believe it will work properly.