Error While taking the input - c

Question

Hey I don't understand why my its taking two inputs while taking the element as input . I tried this code on TurboC compiler , GCC but got the same error .
#include <stdio.h>
int menu();
void bubble_short();
void selection_short();
int main()
{
int ch,j,n,a[100];
ch=menu();
switch (ch)
{
case 1:
{
bubble_short();
break;
}
case 2:
{
selection_short();
}
default :
break;
}
}
void bubble_short()
{
int i,j,n,a[100];
printf("Elements");
scanf("%d",&n);
for (j=0; j<n;j++)
{
scanf("%d",&a[j]);
}
for (i=0;i<n;i++)
{
for (j=0;j<n-1-i;j++)
{
if (a[j]>a[j+1])
{
a[j]=a[j]+a[j+1];
a[j+1]=a[j]-a[j+1];
a[j]=a[j]-a[j+1];
}
}
}
printf("the sorted elements are :\n");
for ( i = 0; i < n; i++)
{
printf("%d\n",a[i]);
}
}
void selection_short()
{
int i,j,n,a[100],min;
printf("Elements");
scanf("%d",&n);
for ( i = 0; i <n-1; ++i)
{
min=i;
for ( j = 1+i; i < n; ++i)
{
if(a[min]>a[j])
min=j;
}
if(i!=min)
{
a[i]=a[i]+a[min];
a[min]=a[i]-a[min];;
a[i]=a[i]-a[min];;
}
}
printf("the shorted elements are :\n");
for ( i = 0; i < n; ++i)
{
printf("%d\n",a[i] );
}
}
int menu()
{
int k;
printf("Enter the choice \n 1. bubble short \n 2. selectionshort");
scanf("\n %d ",&k);
return k;
}
Hey I don't understand why my it's taking two inputs while taking the element as input. I tried this code on TurboC compiler, GCC but got the same error.
Output

Answer 1

Got your problem!
Never use newlines, whitespace, tabs and return carriages inside scanf as to avoid such problems and maintaining good coding guidelines! These act as delimiters for it and you have provided 3 of them.
Edit your menu scanf to this:-
scanf("%d",&k);
A basic logic behind it:- Taking a basic example :-
scanf("%d %d", &i, &j);
Notice that space between two placeholders. When you run this, it will take the first input and then it will wait for that delimiter to be read from the keyboard and afterwards it will read the second parameter of the input.
I think the rest of the program should run fine.

Answer 2

In the menu() function, you have:
scanf("\n %d ",&k);
The leading white space characters (the '\n' and the ' ') are not needed; %d skips leading white space anyway, and one is sufficient. Note that each white space character in a format string for scanf() et al maps to zero or more white space characters in the input.
The trailing white space is bad. It means skip zero or more white space characters (newlines, blanks, tabs) and keep going until you see something that isn't a white space character (or until EOF). Trailing white space in a format string is a bad idea — doubly so when the input is supposed to be interactive. You have to predict what the next input should be before you can terminate the current input, which is not easy for people to do.
There are multiple other issues, too. Your function declarations are not prototypes (you must write int menu(void); etc to make it a prototype in C). You're missing a break after case 2: — it happens to be harmless at the moment, but when you put an error message or another sort option into the system, it becomes a problem. You haven't used enough functions: you should have an array reading function and an array printing function and should use them. You've left the data reading loop out of your selection_short() function. Normally, the term used is sort, not short — the function names seem anomalous to most people.
Your swap algorithm is contorted:
a[i]=a[i]+a[min];
a[min]=a[i]-a[min];;
a[i]=a[i]-a[min];;
You don't need the double semicolons. And you run the risk of overflows if the values are large enough. It's simpler, and far more orthodox — and ultimately safer — to use:
int tmp = a[i];
a[i] = a[min];
a[min] = tmp;
You should check each and every scanf() call to ensure that it succeeded, taking appropriate action if it fails. Note that it can fail by returning 0 or EOF; you should test:
if (scanf("%d", &n) != 1)
…oops…