functions/root.c - Hele rodsøgningsprogrammet. | Lektion 5 - slide 25 : 30 Program 2 |
#include <stdio.h> #include <math.h> int sameSign(double x, double y); double middleOf(double x, double y); int isSmallNumber(double x); double findRootBetween(double a, double b); double f(double x){ /* (x - 5.0) * (x - 3.0) * (x + 7.0) */ return (x*x*x - x*x - 41.0 * x + 105.0); } int main(void){ double x, y; int numbers; do{ printf("%s","Find a ROOT between two number: "); numbers = scanf("%lf%lf", &x, &y); if (numbers == 2 && !sameSign(f(x),f(y))){ double solution = findRootBetween(x,y); printf("\nThere is a root in %lf\n", solution); } else if (numbers == 2 && sameSign(f(x),f(y))) printf("\nf must have different signs in %lf and %lf\n", x, y); else if (numbers != 2) printf("\nBye\n\n"); } while (numbers == 2); return 0; } /* Precondition: The signs of f(a) and f(b) are different */ double findRootBetween(double a, double b){ double l = a, u = b; while (!isSmallNumber(f(middleOf(l,u)))){ if(sameSign(f(middleOf(l,u)), f(u))) u = middleOf(l,u); else l = middleOf(l,u); } return middleOf(l,u); } int sameSign(double x, double y){ return (x > 0 && y > 0) || (x < 0 && y < 0); } double middleOf(double x, double y){ return x + (y - x)/2; } int isSmallNumber(double x){ return (fabs(x) < 0.0000001); }