C function help

[jhendrix]

Hi Im really new to programming and need help with this problem:
Write a C function named root4( ) that returns the fourth root of the argument passed to it.
Thanks.

[Starasoris]

There is a function called sqrt which is in math.h

The forth root is sqrt(sqrt(value));

unless of course you are meant to write your own square root algorithm.

[jhendrix]

Actually it says i need to create a function named root4 which is to take a single double parameter and return the fourth root of the parameter as a double value. I also need to place this function in a loop that will allow the user to input a double value, call root4 with that value, then display the fourth root on the screen and the loop is supposed to continue till a negative number is entered.

If you could show me how to do all this i would greatly appretiate it , thanks

[Banfa]

Use a binary chop method.

NOTE: you can't find the 4th root of a negative number without going into complex arithmatic so for now reject all negative numbers.

In this method you start with a lower limit that is definately too small (0 is good) and a upper limit that is definately too large (the number itself). Then you find a value half way between the 2 numbers and see if this is large or smaller than the root (by multiplying it by itself 4 times and seeing if the result is larger or smaller than the required number). If it is larger you replace the upper limit with the new value and if it is smaller you replace the lower limit. You keep going until the upper and lower limit are the same to a set tolerance.

It is called a binary chop because at each step you discard half the values in the current range so it finds the result fairly quickly.

In steps it is

Let Number be the value we want the root for
Let Tolerance be the tolerance required in percentage

• Set LowerRoot to 0
• Set UpperRoot to Number
• Set Guess = (LowerRoot+UpperRoot)/2
• Set Calc = Guess * Guess * Guess * Guess
• If Calc > Number Then UpperRoot = Guess Else LowerRoot = Guess
• if fabs(UpperRoot - LowerRoot/UpperRoot)*100 < Tolerance Then End Calculation
• Goto 3