how to solve error "stack around variable was corrupted" ?

Hi, i got error in c program. the program is on arithmatic operation, in this output displaying properly, but when i press enter after seeing output then it will show me error like "stack around variable ch was corrupted"

below is my sample code

#include
#include
void Add(int x,int y)
{
printf("%d",x+y);
}
void main()
{
int a;
int b;
char ch;
scanf("%d",&a);
scanf("%s",&ch);
scanf("%d",&b);
switch (ch)
{
case '+':
Add(a,b);
break;
}
getch();
}

so help me how can i solve this ?