no.7.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"

#define ROOT_PRECISION 10e-5
#define PI 3.1415926

float func1(float x)
{
    return (1 / (1 + x*x));
}

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

float sinpson(float a, float b, int n, float (*f)(float x))
{
    float h;
    float s = 0;
    float x;
    int i;
    
    h = ( b - a ) / ( 2 * n );
    x = a;     
    s = f(x);   
    
    for (i = 1; i <= 2 * n - 1; i++) {
        x = x + h;
        if (i % 2)
                s = s + 4 * f(x);
        else
                s = s + 2 * f(x);
    }
    x = x + h;
    s = s + f(x);
    s = s * ( ( b - a ) / ( 6 * n ) );  

    return s;
}

float preciseIntegral(float a, float b, float (*f)(float x), float precision)
{
    float s1, s2;
    int n = 10;
    
    s2 = sinpson(a, b, n, f);
    do {
        n = n * 2;
        s1 = s2;
        s2 = sinpson(a, b, n, f);
    }while ( s2 - s1 > precision || s1 - s2 > precision);
    return s1;
}        
            

int main()
{
    float s;
    s = preciseIntegral(0, 1, func1, ROOT_PRECISION);
    printf("%.5f\n", s);
    s = sinpson(1, 2, 10, func2);
    printf("%.4f\n", s);
    getch();
    return 0;
}