Question

编写一个用矩形法求定积分,这个程序哪里出错了。 答案总是显示0

#include"stdio.h"
#include"math.h"
double
fun1 (double x)
{
return (sin (x));
}

double
fun2 (double x)
{
return (cos (x));
}

double
fun3 (double x)
{
return (exp (x));
}

double
jifen (double (*p) (double x), int a, int b)
{
int i;
double f = 0.0, h, x, y1,y2,area;
h = (b - a) / 10000;
x = a;
y1 = (*p) (x);
for (i = 1; i <= 10000; i++)
{
x += h;
y2 = (*p) (x);
area = y1*h ;
y1 = y2;
f += area;
}
return (f);
}

main ()
{
int a, b, t;
printf ("from which to which?\n");
scanf ("%d%d", &a, &b);
double x = 0.0, y;
printf ("input 1(sin),2(cos),3(exp):\n");
scanf ("%d", &t);
switch (t)
{
case 1:
y = jifen (fun1, a, b);printf ("the answer is %lf\n", y);
break;
case 2:
y = jifen (fun2, a, b);printf ("the answer is %lf\n", y);
break;
case 3:
y= jifen (fun3,a,b);printf("the answer is %lf\n",y);
break;
default:printf("error!\n");
}
}

Answer 1

我这上面测试的时候发现的问题是在
f = (b-a)/10000;这里
因为a,b都是整形，所以如果b-a<10000的话，f的结果都是0的。可以改为
f = (double)(b-a)/10000;先将(b-a)强制转化为double型，就不会出现这个问题了。或者
f = (b-a)/10000.0;这样程序也会自动将(b-a)转化为double型。

这种程序不长，可以试试自己单步调试的。
希望可以帮到你！