float f(float x){ return x*x; }

float Trap(float a, float b, int n, float h){ 
    float integral, x;
    int i; 
    integral = (f(a) + f(b))/2.0; 
    x = a; 
    for (i = 1; i <= n-1; i++) { 
        x += h; 
        integral += f(x); } 
    return integral * h;
}