Loop Run Wrong In Main Function - c

Question

When i run the code,in main function something going wrong.After first round of loop in main,program print "Wrong Choice" altough choice is legal.
#include <stdio.h>
#include <stdlib.h>
int factorial(int n);
void prime_numbers(){
int upper_bound;
printf("Define upper bound:");
scanf("%d",&upper_bound);
printf("Prime Numbers: ");
int i,j;
int variable;
for (i=2;i<=upper_bound;i++)
{
variable = 1;
for (j = 2; j <i; j++)
{ if (i % j == 0)
{
variable = 0;
break;
}
}
if (variable == 1)
printf ("%d ", i );
}
printf("\n");
}
void leibniz_series(){
printf("Define k value:");
int k;
scanf("%d",&k);
double sum=0;
int i;
for (i=1; i<k; i++)
{
if ((i%2)==1)
sum=sum+1.0/((2.0 * (double)i) - 1.0);
else
sum = sum - 1.0/((2.0 * (double)i) - 1.0);
}
printf("Result:%f\n",4*sum);
}
void combination(){
int comb;
printf("Define n and r:");
int n,r;
scanf("%d %d",&n,&r);
comb=factorial(n)/(factorial(r)*factorial(n-r));
printf("Result:%d ",comb);
printf("\n");
}
int factorial(int n){
int f=1;
int i;
for(i=1;i<=n;i++)
f=f*i;
return f;
}
int main()
{
printf("Press P or p for Prime Numbers\n");
printf("Press L or l for Leibniz Series\n");
printf("Press C or c for Combinations\n");
printf("Press E or e for Exit\n");
char choice;
for(;;){
printf("Enter your choice:");
scanf("%c",&choice);
if(choice=='E' || choice=='e')
exit(0);
switch(choice){
case 'p' : prime_numbers();
break;
case 'P' : prime_numbers();
break;
case 'l' : leibniz_series();
break;
case 'L' : leibniz_series();
break;
case 'c' : combination();
break;
case 'C' : combination();
break;
default : printf("Wrong choice\n");
}
}
return 0;
}

Answer 1

It is probably something to do with the return key you pressed to enter the input lying around in your input buffer.
To simply clear that character from the buffer you can read it and ignore it by adding scanf("%*c"); immediately after you scan for a character from the STDIN.
So your new code would look something like this:
printf("Enter your choice:");
scanf("%c",&choice);
scanf("%*c");