While loop repeating function twice in one loop [duplicate] - c

Question

This question already has answers here:
scanf() leaves the newline character in the buffer
(7 answers)
Closed 2 years ago.
the program doesnt stop on scanf("%c", &ch) line. why does it happens sombody can please explain this to me
#include<stdlib.h>
#include<stdio.h>
struct list {
char val;
struct list * next;
};
typedef struct list item;
void main()
{
char ch;
int num;
printf("Enter [1] if you want to use linked list or [2] for realloc\n");
scanf("%d", &num);
if(num == 2)
{
scanf("%c", &ch);
printf("%c", ch);
}
}

Answer 1

Let's say you input 2 when you're reading for num. The actual input stream will be 2\n (\n is the newline character). 2 goes into the num, and there remains \n, which goes into ch. To avoid this, add a whitespace in format specifier.
scanf(" %c", &ch);
This will ignore any whitespaces, newlines or tabs.

Answer 2

The reason behind this is the newline \n character left behind by previous scanf, when pressing Enter key, for the next read of scanf. When the statement
scanf("%c", &ch);
executed then it reads that \n left behind by the previous scanf.
To eat up this \n you can use a space before %c specifier. A space before the %c specifier is able to eat up any number of white-space characters.
scanf(" %c", &ch);
^ a space