对数方程

 

#include <stdio.h>
#include <math.h>
#define EPSILON 1e-7

double bisection(double a, double (*func)(double, double));
double f(double a, double x);
int main() {
    double a;
    scanf("%lf",&a);
    printf("%lf\n", bisection(a, f));
    return 0;
}

double bisection(double a, double (*func)(double, double)) {
    double p=-a,q=a;
    double mid=(p+q)/2;
    while(fabs(f(a,mid))>EPSILON){
        if(f(a,p)*f(a,mid)<0) q=mid;
        else p=mid;
        mid=(p+q)/2;
    }
    return mid;
    
    
    
}

double f(double a, double x) {
    return ( x + log(x) - a) ;
}