Need help with C++ integration problem

I have an assignment where I have to use the trapezoidal and simpson's rules to estimate the integral of a function. Everything works as far as I can tell, except for the final results. If someone could help me out, it would be much appreciated.

Code:

#include<stdio.h>
#include<math.h>
#include<stdlib.h>
#include<conio.h>

//Declare global variables
double A, B, x=0, n1, n2;
char ch;

//Function to evaluate both of the functions
double evalf(double x){
       if(ch == 'a')
          return(sin((2*x)/5) - x + 1);
       else
          return(cos((2*x)/5) + (3*x) + 1);
       }

//Function to input the number of intervals wanted for the Trapezoidal rule,
//and see if their accuracy is acceptable.
double trap_intervals(){
   double accuracy=0, error=1, h, n;
   while(error > accuracy){
      printf("\nPlease enter the number of subintervals you would like: ");
      scanf("%lf", &n);
      printf("Please enter the accuracy you would like: ");
      scanf("%lf", &accuracy);
      h = (B-A)/n;
      error = ((B-A)*(h*h)*sin(2*B/5))/75;
      if(error < 0)
         error = -error;
      if(error > accuracy)
         printf("\nSorry, you do not have enough subintervals for the level of accuracy.");
      printf("\nYour error is %lf.\n", error);
   }
   return(n);
}

//Function to estimate the integral of the function using the Trapezoidal Rule
double trapezoid(){
       double X, Y, p, h, x, sum;
       h = (B-A)/n1;
       X = evalf(A);
       Y = evalf(B);
       for(x=(A+h); x<B; x+=h){
          p = evalf(x);
          sum+=p;
       }
       return(h*((1/2)*X + sum + (1/2)*Y));
}

//Function to input the number of intervals wanted for Simpson's rule, and see
//if their accuracy is acceptable.       
double simp_intervals(){
   double accuracy = 0, error = 1, h, n;
   while(error > accuracy){
      printf("\nPlease enter the number of subintervals you would like: ");
      scanf("%lf", &n);
      printf("Please enter the accuracy you would like: ");
      scanf("%lf", &accuracy);      
      h = (B-A)/n;
      error = (-4*(B-A)*(h*h*h*h)*sin(2*B/5))/28125;
      if(error<0)
         error= -error;
      if(error > accuracy)
         printf("\nSorry, you do not have enough subintervals for the level of accuracy.");
      printf("\nYour error is %lf.\n", error);
   }
   return(n);
}     

//Function to estimate the integral of the function using Simpson's Rule
double simpson(){
       double X, Y, x, p, q, h, sum1, sum2;
       int i;
       h = (B-A)/n2;
       X = evalf(A);
       Y = evalf(B);
       for(x=A+h; x<B; x+=h){
        i = 1;
        if(i%2 == 0){
           p = 2*evalf(x);
           sum1+=p;
           }
        else{
           q = 4*evalf(x);
           sum2+=q;
           }
        i++;
        }
        return((h/3)*(X + sum1 + sum2 + Y));
}
           
//Main function starts here.
int main(){
    
   double temp;

//Decide which function you wish to integrate
   printf("If you want to integrate the function f(x) = sin(2x/5) - x + 1, press 'a'.");
   printf("\nIf you want to integrate the function f(x) = cos(2x/5) + 3x + 1, press 'b'.\n");
   scanf("%c", &ch);
   
//Ensure the user only picks a or b
   while(ch != 'a' && ch != 'b'){
      printf("\nSorry, invalid input. Please try again:\n");
      scanf("%c", &ch);
   }

//Tell the user which function will be integrated
   if(ch == 'a')
      printf("\nThe function we are integrating is f(x) = sin(2x/5) - x + 1.\n");
   else
      printf("\nThe function we are integrating is f(x) = cos(2x/5) + 3x + 1.\n");

//Choose the intervals, swap A and B if A is greater than B
   printf("Please enter the values of the interval [A,B].\nA: ");
   scanf("%lf", &A);
   printf("\nB: ");
   scanf("%lf", &B);
   if(A>B){
      printf("\nA is larger than B. Swapping values now...");
      B = temp;
      A = B;
      temp = A;
      temp = 0;
   }

//Pick intervals for Trapezoidal Rule
   printf("\nWe must now enter the number of intervals for the trapezoidal rule.");
   n1 = trap_intervals();

//Pick intervals for Simpson's Rule
   printf("\nWe must now enter the number of intervals for Simpsons rule.");
   n2 = simp_intervals();

//Estimate the value of the integration using the Trapezoidal Rule
   temp = trapezoid();
   printf("\nThe value of integration using the trapezoidal rule is %lf.", temp);
   temp = 0;

//Estimate the value of the integration using Simpson's Rule
   temp = simpson();
   printf("\nThe value of integration using Simpson's rule is %lf.", temp);

//End program
   printf("\n\nPress any key to finish...");
   getch();
}

Basically the problem is in the trapezoid and simpson functions, sorry for pasting the whole code.

What C++? All I see is C!

First, learn to write code without unnecessary Global Variables.
Second, learn to swap two value correctly.
Third, learn to post C code in the C sub-forum.

Code:

   if(A>B){
      printf("\nA is larger than B. Swapping values now...");
      B = temp;
      A = B;
      temp = A;
      temp = 0;
   }

Tim S.