Finding an Interval That Include A Root of any Polynomial

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define in printf("\n")
double func(double x,double *coef,int order);
double coefs(double *a,int order);
double writ(double *a,int mag);
double seepol(double *a,int order);
double findinterval(double xleft,double xright,double stepsize,double x,double *coef,int order);
int main()
{
int order,cont;
double x,xleft,xright,stepsize;
printf("please enter the order of polynomial ");
scanf("%d",&order);
system("cls");
printf("The order is %d.",order);
in;
in;
double coeff[order];
coefs(coeff,order);
in;
system("cls");
printf("You create this polynomial");
in;
seepol(coeff,order);
in;
printf("To find the possible interval that include a root push '1'");
in;
in;
printf("To find the value of polynomial at any point push ''0''");
in;
scanf("%d",&cont);
if(cont==0){
in;
system("cls");
printf("You create this polynomial");
in;
seepol(coeff,order);
in;
printf("Tell us the value that you want to find?");
in;
scanf("%lf",&x);
system("cls");
printf("You create this polynomial");
in;
seepol(coeff,order);
in;
printf("f(%lf)=%lf",x,func(x,coeff,order));
}else if(cont==1){
system("cls");
system("cls");
printf("You create this polynomial");
in;
seepol(coeff,order);
in;
in;

printf("Please Tell us The interval that you want to check");
in;
printf("First down point ?");
scanf("%lf",&xleft);
printf("Up point? ");
scanf("%lf",&xright);
printf("Tell us stepsize");
scanf("%lf",&stepsize);
in;
findinterval(xleft,xright,stepsize,x,coeff,order);
}else
printf("Please do not kid with me");

return 0;
}

double func(double x,double *coef,int order)
{
int i;
double sum=0.0;
for(i=0;i<=order;i++)
sum=sum+((*(coef+i))*pow(x,i));
return sum;
}
double coefs(double *a,int order){
int i;
printf("Please Enter The Coefficients of Polynomial");
in;
in;
printf("From least order's coefficent to most");
in;
in;
for(i=0;i<=order;i++){
printf("%dth element coefficient is\t",i+1);
scanf("%lf",(a+i));
}
}
double writ(double *a,int mag){
int i=0;
while(i<mag){
printf("%lf",*(a+i));
in;
i++;
}
}
double seepol(double *a,int order)
{
int i=order;
printf("f(x)=");
while(i>=0){

printf("%.2lf",*(a+i));
if(i!=0)
printf("*x^%d ",i);
if(i!=0)
printf("+");
i--;
}
}

double findinterval(double xleft,double xright,double stepsize,double x,double *coef,int order){

double xend=xright;
xright=xleft+stepsize;

while(xleft<xend && (func(xleft,coef,order)*func(xright,coef,order))>0 )
{

xleft=xright;
xright=xright+stepsize;
if(xright>xend)
xright=xend;
}

if(func(xleft,coef,order)*func(xright,coef,order)>0){
in;
printf("No root in this interval");
in;
}


if(func(xleft,coef,order)*func(xright,coef,order)<0){

printf("There is a root between [%lf  %lf]",xleft,xright);
in;


}

}