>>551
// ∫[a,b] |cos(x)|dx の意味だと解釈して
#include <stdio.h>
#include <math.h>

double f(double x) {
return abs(cos(x));
}

int integral(double a, double b)
{
int i;
int n = 100;
double h = (b - a) / n;
double sum = 0.0;
for (i = 0; i < n; i++) {
double x = a + h * i;
sum += (f(x) + f(x+h)) / 2;
}
return sum;
}

int main()
{
printf("%f\n", integral(0, 3.14));
return 0;
}