Question

Edit question

Miscellaneous C knowledge. (Put all answers in the same q5.txt file, they’re all short.)

(a) [2 marks] On an old 16-bit computer system and its C compiler,sizeof(double)=8andsizeof(int)=2. Given the two type definitions below, what weresizeof(s)andsizeof(lingling)on that system? Assume that ins, there is no gap between the twofields.

typedef struct s {

double r[5];int a[5];

} s;

typedef union lingling {

double r[5];int a[5];

} lingling;

(b) [2 marks] Given the following declarations, two questions: What is the type ofq? Whatis the type ofy?double* p, q;typedef

double *t;t x, y;

(c) [1 mark] To read a character from stdin, what’s wrong with “c = getchar();”, ifchasbeen declared with “char c;”?

(d) [3 marks] A beginner in C has coded up an attempt to determine whether stdin isempty:

#include <stdio.h>

int main(void){

if (feof(stdin)) {

printf ("empty\n");

   else {

printf ("not empty\n");

}

return 0;

}

This is run with stdin redirected from an empty file. It mistakenly reports “not empty”.Help the beginner by briefly answering: Why is this approach ineffective? And what isa correct approach?

Answer 1

Question a)
Given:
sizeof(double)=8 and sizeof(int)=2

typedef struct s {
double r[5];int a[5];
} s;

typedef union lingling {
double r[5];int a[5];
} lingling;

To find size of s and size of lingling

For s:
There are 5 double values=>5*8=40
There are 5 int values=>10
sizeof(s)=40+10=50

sizeof(s)=40

For lingling:

union is also like structure but it returns the max size among the variables used
There are 5 double values=>5*8=40
There are 5 int values=>10
sizeof(lingling)=max(40,10)=40

sizeof(lingling)=40

Question b)

Given

double* p, q;
typedef double *t;t x, y;

To find the type of q and type of y.

q is of type double.
y is of type t which is an alias for a pointer for type double

So y is pointer of double type.

Question c)

To read a character from stdin, what’s wrong with “c = getchar();”, if c has been declared with “char c;”?

For reading character from stdin there has to be an input.if not get char will return EOF.

Question d)

The EOF returns a boolean value in C.

If the value is 0 then there is no data.

Otherwise The data will be read.

SO the obvious code is

#include <stdio.h>
int main(void){
if (feof(stdin)==0) 
{
        printf ("empty\n");
}
else 
{
        printf ("not empty\n");
}
return 0;
}

This will print correctly as empty or not empty