no.6.c

中南大学C语言程序设计实习 1 实验一：C语言图形模式的设置 2 实习二：一元函数的图形绘制 3 实习三：二维图形的几何变换 4 实习四：非线性方程求根的二分法 5 实习五

#include "stdio.h"
#include "conio.h"
#include "math.h"
#define ROOT1_PRECISION 10e-3
#define ROOT2_PRECISION 10e-5
#define PI 3.1415926

enum {trapezia, rectangle};

float func1(float x)
{
    return (sin(x) / x);
}

float func2(float x)
{
    return (1 / (1 + x*x));
}   

float integral(float a, float b, int n, float (*f)(float x), int type)
{
    float h;
    float r = 0;
    float ox, x;
    int i;
    
    h = ( b - a ) / n;
    x = a;        
    
    for (i = 1; i <= n; i++) {
        ox = x;
        x = x + h;
        if (type)
                r = r + f( (ox + x) / 2 );
        else    
                r = r + ( f(ox) + f(x) ) / 2;
    }
    r = r * h;
    return r;
}

float preciseIntegral(float a, float b, float (*f)(float x), int type, float precision)
{
    float s1, s2;
    int n = 10;
    s2 = integral(a, b, n, f, type);
    
    do {
        n = n*n;
        s1 = s2;
        s2 = integral(a, b, n, f, type);
    }while ( s2 - s1 > precision || s1 - s2 > precision);   
    return s1;
}    


int main()
{
    float s;
    s = preciseIntegral(1, 2, func1, rectangle, ROOT1_PRECISION);
    printf("func1 rectangle =%.3f\n", s);
    s = preciseIntegral(1, 2, func1, trapezia, ROOT1_PRECISION); 
    printf("func1 trapezia =%.3f\n", s);
    
    s = preciseIntegral(0, 1, func2, rectangle, ROOT2_PRECISION);
    printf("func2 rectangle =%.5f\n", s);
    s = preciseIntegral(0, 1, func2, trapezia, ROOT2_PRECISION); 
    printf("func2 trapezia =%.5f\n", s);
    printf("PI / 4 =%.5f\n", PI / 4);
    
    getch();
    return 0;
}