C Programming - Control Instructions - Discussion

#include<stdio.h>
int main()
{
int a = 10, b;
a >=5 ? (b=100): (b=200);
printf("%d\n", b);
return 0;
}
gives the output 100 on the online compilar which is provided by this site
check it my friends

Aloke would you please explain your program ? How does it work ?

@Mani

The program which Aloke has posted works even though the expression a >=5 ? (b=100): (b=200); is not assigned to any value .. Would you please explain us in detail if you are clear with the concept ?

Answer must be 100; because a=10 thats are >a. But please help me about lvalue value.

It gives output b = 200 on DOSBox c++ when the expression is
a >=5 ? b=100: b=200;
In above expression.if you change a>=11/12 or anything.
Ouptut is b = 200. any condition doesn't make any difference to this answer.

When expression is a >=5 ? (b=100): (b=200);
It gives output b = 100;

Nowhere error is coming, please somebody explain me

Actually when we use conditional operators we should store the condition result in any variable. see below example.
#include<stdio.h>
{
int a=10, b;
b= a>=5?100:200;
printf("%d", b);
}
RESULT:
100

The above given question should be like i have stated here.

#include<stdio.h>
{
int a=10, b;
a>=5?100:200;
printf("%d", b);
}
RESULT:
ERROR


According to the given question answer should be 100 not error because b value will be assigned if condition is true or false.

What is the meaning of ? in between the a>=5 and b=100.

The conditional operator (?:) always return either true part or false part. Lvalue means legal left value. There no need of Lvalue in conditional operator so the program executes successfully and gives output 100;.

Condition is satisfying, hence b=100 will be assigned to b and it becomes print 100?

L value error is found because if you are writing a>=5?b=100:b=200;

Then in last assignment b=200,the value 200 is assigned to left side,which is not correct as per C-language Rule.

Hence,the above problem can be removed by using parenthesis on b=100 and b=200 [like (b=100) and (b=200)].

On other side,if you use expression as:

b=a>=5 ? b=100: b=200;

Then again it will show the same error because of same reason.

But expression is correct if you use:
b=a>=5 ? (b=100): (b=200);

Output is 100 when you use parenthesis.
Compiler used : Dev C++ version 5.4.1 Portable.