if else condition with and operator

Question

void main()
{
int i=4,j=12;
if(i=5 && j>5)
    printf("Hi!");
else
        printf("Hello!");
}

First of all,the output of the above code is Hi!.Acording to me it should show a syntax error as i=5 is an assingment operator not i==5,if i==5 then also it is false and should print Hello,but how could it print Hi?

Why do you ignore compiler warnings? If your compiler does not warn, instantly get a modern compiler! And as you say: "`=` is an assignment **operator**" — too honest for this site, May 29 '17 at 20:54

Vlad from Moscow · Answer 1 · 2017-05-29T21:09:28.907

The condition in the if statement

if(i=5 && j>5)

is equivalent to

if( i = ( 5 && j>5 ))

As 5 is not equal to 0 and j is indeed greater than 5 then the expression ( 5 && j>5 ) evaluates to 1 and is assigned to the variable i.

From the C Standard (6.5.16 Assignment operators)

3 An assignment operator stores a value in the object designated by the left operand. An assignment expression has the value of the left operand after the assignment...

So as the value of the variable i is equal to 1 then the if condition is executed.

It seems you mean

if(i==5 && j>5)
   ^^^^

Take into account that according to the C Standard the function main without parameters shall be declared like

int main( void )

Good for pointing out what may be an unexpected value assigned to `i`. — ad absurdum, May 29 '17 at 21:04

Govind Parmar · Answer 2 · 2017-05-29T20:58:06.003

0

i=5 is a perfectly valid expression to put in a conditional, even if it's not a test for equality. That assignment produces a value that isn't zero, so the condition is still true.

edited May 29 '17 at 20:58

answered May 29 '17 at 20:53

Govind Parmar

20,656
7
53
85

@EugeneSh. some compilers will. There's no guarantee though. – Govind Parmar May 29 '17 at 20:54
1

Note that due to operator precedence, `i = 5` is not evaluated in OP code; rather the result of `5 && j>5` is assigned to `i`. – ad absurdum May 29 '17 at 21:13
2

@DavidBowling Agreed, but either way, the point is - an assignment in an `if()` statement is valid C. – Govind Parmar May 29 '17 at 21:55

score 0 · Answer 3 · answered May 29 '17 at 21:08

0

You can assign variables in condition parameters like

While((a=b)!=null){
    ...
)

Try to output every variable (i,j) to see whats going on

answered May 29 '17 at 21:08

Amir Reza Mohammadi

76
7

if else condition with and operator

3 Answers3