Bisection Method (Predefined function)

#include<stdio.h>
#include<conio.h>
#include<math.h>

float function(float);

int main(){
    float a, A,b, B, c, C, tc, m;
    printf("Enter the two intial range:\n");
    scanf("%f%f",&a,&b);
    A=function(a);
    B=function(b);
    if((A*B)>0){
        printf("\n\nPlease enter valid range.");
        main();
    }
    tc=a;
    do{
        c=(a+b)/2;
        C=function(c);
        if((function(a)*function(c))<0){
            b=c;}
        else{
            a=c;}
        m=tc-c;
        tc=c;
    }while(fabs(m)>0.0009);
    printf("\n\nThe root is: %.4f",c);
    getch();
}

float function(float x){
    return((x*x)-(4*x)-10);
}