程序代码：

#include<stdio.h>
#include<math.h>
float integral(float a, float b, int n, float(*fun)(float x))
{
    int i;
    float x, h, s;
    h = (b - a) / n;
    x = a;
    s = 0;
    for (i = 1; i <= n; i++)
    {
        x = x + h;
        s = s + (*fun)(x)*h;
    }
    return s;
}

float fsin(float x)
{
    return sin(x);
}

float fcos(float x)
{
    return cos(x);
}

float fexp(float x)
{
    return exp(x);
}

int main()
{
    float integral(float a, float b, int n, float(*fun)(float));
    float fsin(float x);
    float fcos(float x);
    float fexp(float x);
    float a1 = 0, b1 = 1, a2 = -1, b2 = 1, a3 = 0, b3 = 2, n = 20;
    printf("f1=%5.2f\n", integral(a1, b1, n, fsin));
    printf("f2=%5.2f\n", integral(a2, b2, n, fcos));
    printf("f3=%5.2f\n", integral(a3, b3, n, fexp));
    return 0;
}