Integrating function using trapezoidal rule

Hi guys, can some one please help me with this program. I need to be able to integrade a function but i seem to be having some trouble getting consistant result using the rule. more specifically im not getting consistant result for the sub intervals i am implementing. Im thinking that my for loop needs to be modified to make this work, but i dont know how... that is.. the intergration of y=x from 0 to 10 is 50, but as you can see from the output i only get that for the first interval mainly 10.

Code:

#include<stdio.h>
#include<math.h>
#define F(X) X
int main(){
int i,k1,k2;
double a,b,h1,h2,sum=0,sum2=0,U1,U2,y;
printf("Enter the lower limit:");
scanf ("%lf",&a);
printf("Enter the upper limit:");
scanf("%lf",&b);

k1=10;
k2=20;
printf("%5s %5s %12s %12s %12s\n","k1","k2","U1","U2","y");
while(k1<=1250 && k2<=2500){
h1=(b-a)/k1;
for (i=1;i<=k1-1;i++){sum=sum+F(a+(i*h1)); }
U1=(h1/2)*(F(a)+2*sum+F(b));

h2=(b-a)/k2;
for (i=1;i<=k2-1;i++){sum2=sum2+F(a+(i*h2)); }
U2=(h2/2)*(F(a)+2*sum2+F(b));

y=( (2*2*U2)/((2*2)-1) )-( U1/((2*2)-1) );

printf("%5d %5d %12.6lf %12.6lf %12.6lf\n",k1,k2,U1,U2,y);

k1+=(5*k1)-k1;
k2+=(5*k2)-k2;

}






return 0;
}

can someone please help me.

and sorry to the modes for not knowing the proper tags

sorry just to clarify.. the out put shoudl be 50 for all sub intervals

never mind guys.. i needed to reinitialized sum and sum to back to 0 in the while.. thanks though