C Program for Bisection Method

Bisection method:

#include "stdio.h"

#include "conio.h"

#include "stdlib.h"

#include "iostream.h"

int fn[20];

int n;

double a,b,x0;

double fnval;

float abso(float x)

{

        if (x<0) return -x;else return x;

}

double power(double a,int b)

{

        int i;

        double c=1;

        for (i=0;i<=b;i++)

c=c*a;

        return c;

}

void getfunction()

{

        int i;

        printf("Enter the degree of the function: ");

        cin >> n;

        printf("\nStart entering the coefficients\n\n");

        for (i=n;i>=0;i--)

        {

               printf("Enter coefiicient of degree %d: ",i);

               cin >> fn[i];

        }

}

void displayfunction()

{

        int i;

        printf("\nCurrent function is:\n ");

        for (i=n;i>-1;i--)

        {

               if (i==0) printf("%d",fn[i]);

               else printf("%dx^%d + ",fn[i],i);

        }

}

float getaccuracy()

{

        float no;

        printf("\nEnter the accuracy required: ");

        cin >> no;

        return no;

}

double fx(double x)

{

        int i;

        double ans=0;

        for (i=n;i>-1;i--)

        {

               ans=ans+fn[i]*power(x,i);

        }

        return ans;

}

void getinitialvals()

{

        float curr=0,prev=0;

        static float left=-100;

        for (int i=left;i<=100;i++)

        {

               curr=fx(i);

               a=i-1;b=i;

               if (curr==0)

               {

                       left=i+1;

                       printf("\nroot is %f",b);

                       getinitialvals();

               }

               if (i==99)

               {

                       printf("\n\nThe equation has no further real roots");

                       exit(1);

               }

               if (curr*prev<0)

               {

                       left=i;

                       break;

               }

               prev=curr;

        }

}

void checkinivals()

{

        if(fx(a)>fx(b))

        {

               double temp=a;

               a=b;

               b=temp;

        }

}

int main()

{

        int i=0,itr=0;

        int j=1;

        clrscr();

        getfunction();

        float accu=getaccuracy();

        displayfunction();

        do

        {

               i=0;

               getinitialvals();

               checkinivals();

               cout << "\n\nInitial values are "<< a<< " and " << b << "\n";

               do

               {

                       x0=(a+b)/2;

                       fnval=fx(x0);

                       printf("%d%15f%15f%15f%15f%15f\n",i+1,a,b,x0,fnval,b-a);

                       if (fnval<0) a=x0; else b=x0;

                       i++;

               } while (abso(b-a)>accu);

               printf("\n\nThe root of the equation is %f in %d iterations",x0,i);

               printf("\nPress any key to search for more roots");

               getch();

        } while(1);

}