Question

Following program gives error

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

the error is

ka1.c: In function ‘main’:
ka1.c:5: error: lvalue required as left operand of assignment

now if I replace the line

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

by

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

and then compile then there is no error.
So I wanted to know what is wrong with

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

Answer 1

The ternary operator (?:) has higher precedence than the assignment operator (=). So your original statement is interpreted as:

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

Write it like this instead:

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

This is idiomatic C. (The brackets around the condition are not really necessary, but they aid readability.)