pre and post increment

[matangi]

int main()
{
int a=5,s;
s=++a + ++a;
printf("%d",a);
printf("%d",s);
}

output is 7 and 14

BUT

int main()
{
int a, s;
printf("Enter value of a");
scanf ("%d",&a);
s=++a + ++a;
printf("%d",a);
printf("%d",s);
}

input user gives is 5
output is 7 and 13

WHY?

[zahraZ]

hello,
i test your codes but they have same result!(7 & 14)

[newb16]

Because the result of ++a + ++a is undefined per the language standard. (see two similar topics below). Value of 'a' is guaranteed to be 7 after evaluating of this expression.