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

double a, b;//定義全域性變數，傳遞區間值，可嘗試指標

double get_num(double m) {
    double f;
    f = m * m + 7 * m - 9;
    return f;
}

double search_num(double x1, double h) {
    double x2, x3;
    double y1, y2, y3;
    x2 = x1 + h;
    y1 = get_num(x1);
    y2 = get_num(x2);
    
 
//遞減區間
    if (y1 > y2)
    {
        h = 2 * h;
        x3 = x2 + h;
        y3 = get_num(x3);

        if (y2 > y3) {
            h = h;
            while (!(y2 < y3))
            {
                x1 = x2;
                y1 = y2;
                x2 = x3;
                y2 = y3;
                x3 
 
= x2 + h;
                y3 = get_num(x3);
            }
        }
        printf("區間為：[%.3f,%.3f]\n", x1, x3);
        a = x1; b = x3;
        printf("%.3f,%.3f,%.3f\n", y1, y2, y3);
    }
    //遞增區間,反向搜尋
    if (y1 < y2)
    {
        double temp;
        temp = x1;
        x1 = x2;
        y1 = y2;
        x2 
 
= temp;
        y2 = get_num(x2);
        x3 = x2 - 2 * h;
        y3 = get_num(x3);

        if (y2 > y3) {
            while (!(y2 < y3))
            {
                x1 = x2;
                y1 = y2;
                x2 = x3;
                y2 = y3;
                x3 = x2 - h;
                y3 = get_num(x3);
            }
        }
        printf("區間為：[%.3f,%.3f]\n", x1, x3);
        a = x1; b = x3;
        printf("%.3f,%.3f,%.3f\n", y1, y2, y3);
    }
    return a,b;
}
void fen_ge(double m, double n) {
    double s = 0.618;
    double m1, n1;
    double y1, y2;
    double temp;
    double q = 0.1;//定義精度
    m1 = n - s * (n - m);
    n1 = m + s * (n - a);
    y1 = get_num(m1);
    y2 = get_num(n1);    
    
    while (1)
    {
        if (y1 >= y2) {
            m = m1;
            m1 = n - s*(n - m);
            n1 = m + s*(n - m);
            y1 = get_num(m1);
            y2 = get_num(n1);
        }
        else
        {
            n = n1;
            m1 = n - s*(n - m);
            n1 = m + s*(n - m);
            y1 = get_num(m1);
            y2 = get_num(n1);
        }
        temp = (double)abs(n - m);
        if (temp < q)
        {
            printf("%f,%f\n,%f,%f\n", m, n, y1, y2);
            break;
        }
    }
    return 0;
}


void main()
{
    search_num(10.0, 0.5);    
    fen_ge(a, b);
    return 0;
}

輸出結果如下：