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(); }