2.c

#include "math.h"
#include "stdio.h"

double lrgs(a,b,eps,f)
double a,b,eps,(*f)();
{
    int m,i,j;
    double s,p,ep,h,aa,bb,w,x,g;
    double t[5]={-0.9061798459,-0.5384693101,0.0,0.5384693101,0.9061798459};
    double c[5]={0.2369268851,0.4786286705,0.5688888889,0.4786286705,0.2369268851};
    m=1;
    h=b-a; s=fabs(0.001*h);
    p=1.0e+35;ep=eps+1.0;
    while ((ep>=eps)&&(fabs(h)>s))
    {
        g=0.0;
        for (i=1;i<=m;i++)
        {
            aa=a+(i-1.0)*h; bb=a+i*h;
            w=0.0;
            for (j=0;j<=4;j++)
            {
                x=((bb-aa)*t[j]+(bb+aa))/2.0;
                w=w+(*f)(x)*c[j];
            }
            g=g+w;
        }
        g=g*h/2.0;
        ep=fabs(g-p)/(1.0+fabs(g));
        p=g; m=m+1; h=(b-a)/m;
    }
    return (g);
}
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///////////////////////////////////////////////////////////////////////////////
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double c;
double bb(x)
double x;
{
    double y;
    y=c*x*x;
    return (y);
}

///////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
main()
{
    double a,b,eps,g,bb(double);
    a=0.0;b=2*3.1415926;eps=0.000001;
    c=1;
    g=lrgs(a,b,eps,bb);
    printf("\n" );
    printf("g=%13.5e\n", g);
    printf("\n" );

    c=2;

    g=lrgs(a,b,eps,bb);
    printf("\n" );
    printf("g=%13.5e\n", g);
    printf("\n" );
}