lvalue error on the 10th line

Question

#include <stdio.h>
#include <conio.h>
void main ()
{
    clrscr ()   ;
    char a  [5];
    puts ("K?");
    gets (a);
    fflush (stdin);
    if (a = ("K"))
    {
        puts (a);
    }
    else
    {
        puts ("BAE");
    }
    getch ();
}

The 10th line shows an Lvalue error while compiling, please help. this is my first program ever and this is my first day ever on coding and I'm self teaching.

score 1 · Answer 1 · edited May 23 '17 at 12:28

1

fflush(stdin) is Undefined Behavior
the comparison operator in C is a ==; = is the assignment operator. You can't assign anything to an array, so an error is thrown
you can compare strings using strcmp() from <string.h>; == just compares their addresses

edited May 23 '17 at 12:28

Community

1
1

answered Apr 02 '15 at 16:34

cadaniluk

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Thanks, the code compiles now but whatever I type, the result is "BAE" instead of (a). please help. – SirVirgin Apr 02 '15 at 16:40
`strcmp()` returns `0` if the strings equal. You sure you tested that? – cadaniluk Apr 02 '15 at 16:41
Oh I'm a retard, I get it. Got it working now. Thanks! – SirVirgin Apr 02 '15 at 16:43
On StackOverflow, you thank by accepting an answer. But you're welcome anyway. ;-) – cadaniluk Apr 02 '15 at 16:53

score 0 · Answer 2 · answered Apr 02 '15 at 16:36

0

I think that instead of the assignment in the if statement

if (a = ("K"))

you mean a comparison.

Nevertheless arrays do not have the comparison operator. You have to compare arrays element by element yourself. For character arrays there is function strcmp declared in header <string.h>. Thus the valid code can look like

Also you should not use fflush function with standard input. Otherwise the program has undefined behaviour,

#include <string.h>

//...

if ( strcmp( a, "K" ) == 0 )
//...

answered Apr 02 '15 at 16:36

Vlad from Moscow

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Arrays **do** have a comparison operator when they are implicitly converted into an address. – cadaniluk Apr 02 '15 at 16:44
@cad You are wrong. Arrays do not have the comparison operator., It is pointers that have the comparison operator., Pointers and arrays are different types. – Vlad from Moscow Apr 02 '15 at 16:45

score 0 · Answer 3 · answered Apr 02 '15 at 16:41

There are two mistakes in this line

if (a = ("K"))

First, you are using = where you meant ==. But that is wrong anyway, you cannot test for string equality in C. It has to be something like this, which tests the first character of the string and its terminator

if (a[0] == 'K' && a[1] == '\0')

or, you can use a library function

#include <string.h>
...
if (strcmp(a, "K") == 0) {
    // are the same string.
}

lvalue error on the 10th line

3 Answers3