Secant method – Roots of Non-Linear Equation | FORTRAN 95

PROGRAM secant
IMPLICIT NONE
REAL::f,ea=6,es=1,x0,x1,x2
INTEGER::c=0

PRINT *, "============================================" 
PRINT *, "PROGRAM TO FIND ROOTS USING - SECANT METHOD [BY - www.BottomScience.com]" 
PRINT *, "============================================"

PRINT *,'Initial approximation?'
read(*,*)x0,x1

DO WHILE(ea>es)
x2=x1-((x1-x0)/((f(x1))-(f(x0))))*f(x1)
ea=abs(((x1-x0)/x1)*100)

x0=x1
x1=x2
c=c+1

IF(c>50) EXIT

PRINT *,'Current root is',x1
WRITE(1,*) x1
END DO

IF(x1 > 3E+38 .OR. x1 < -3E+38) THEN

PRINT *,'WRONG INTIAL APPROXIMATION'
ELSE
PRINT *,'FINAL ROOT IS',x1
END IF

END PROGRAM

REAL function f(x1)

REAL::x1

f=(x1**2)-3

RETURN
END FUNCTION