Lvalue required error in C

Question

my code is:

#include<stdio.h>
int main() {
   int a=10, b;
   a >= 5 ? b=100 : b=200;
   printf("%d %d", a, b);
   return 0;
}

Here comes a "Lvalue Required" in the line of conditional operator.

Can you explain me why?

By the way, the same program is perfectly working in C++.

Answer 1

The idiomatic way to write that assignment is:

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

If you insist on keeping it your way, add parentheses:

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

For details on why this works in C++ but not in C, see Conditional operator differences between C and C++ (thanks @Grijesh Chauhan!)

Answer 2

parenthesis have the higher precedence in C.. U get the warning due to precedence problem.. Try this..

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