sum.c

这是一个计算积分的程序

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

// #define f(x) (sqrt(1 - exp(-x)) / x)

// #define f(x) sqrt(4 - sin(x) * sin(x))
// #define PI 3.1415926535897932384626433832795

// #define f(x) (x * exp(x) / (1 + x) / (1 + x))

float f(float x)
{
	return sqrt(1 - exp(-x)) / x;
}

float sumS(float a, float b, int n, float *x)
{
	float tmp1, tmp2;
	int i;
	tmp1 = 0; tmp2 = 0;
	n /= 2;
	for(i = 0; i <= n - 1; i++)
	{
		tmp1 += f(x[2 * i + 1]);
	}
	tmp1 *= 4;
	for(i = 1; i <= n - 1; i++)
	{
		tmp2 += f(x[2 * i]);
	}
	tmp2 *= 2;
	return (b - a) / 6 / n * (f(a) + tmp1 + tmp2 + f(b));
}

float sumT(float a, float b, int n, float *x)
{
	float tmp;
	int i;
	tmp = 0;
	for(i = 1; i <= n - 1; i++)
	{
		tmp += f(x[i]);
	}
	tmp *= 2;
	return (b - a) / 2 / n * (f(a) + tmp + f(b));
}


void main(void)
{
	int i, n;
	float a, b, h;
	float* x; 
	float s, t;
	printf("a="); scanf("%f", &a);
	printf("b="); scanf("%f", &b);
// 	a = 0; b = PI / 6;
	printf("n="); scanf("%d", &n);
	n *= 2;
	h = (b - a) / n;
	printf("h=%f\n", h);
	x = (float*)calloc(n + 1, sizeof(float));
	for(i = 0; i <= n; i++)
	{
		x[i] = a + i * h;
	}
	for(i = 0; i <= n; i++)
	{
		printf("x%d=%f\tf(x%d)=%f\n", i, x[i], i, f(x[i]));
	}
	s = sumS(a, b, n, x);
	t = sumT(a, b, n, x);
	printf("t%d=%f\n", n, t);
	printf("s%d=%f\n", n / 2, s);
}