>>381 台形則
#include<stdio.h>
#include<math.h>

#define PI 3.1415926535897932384626433832795

double f(double x){
return cos(5*sin(2*PI*x+1));
}
double integral(double (*f)(double), double s, double e, long div){
long i;
double x, delta, sum;

delta=(e-s)/div;
sum=(f(s)+f(e))/2;
for(i=1;i<=div-1;i++){
x=s+delta*i;
sum+=f(x);
}
sum*=delta;
return sum;
}
int main(void){
long i, div;
FILE *fp=stdout;

for(i=0;i<=20;i++){
div=1<<i;
fprintf(fp, "div=%ld integral=%g\n", div, integral(f, 0.0, 1.0, div));
}
return 0;
}