Comma operator should be used carefully

In C and C++, comma is the last operator in precedence table. So comma should be carefully used on right side of an assignment expression. For example, one might expect the output as b = 10 in below program. But program prints b = 20 as assignment has higher precedence over comma and the statement “b = 20, a” becomes equivalent to “(b = 20), a”.

#include<stdio.h> 
int main() 
{ 
  int a = 10, b; 
  b = 20, a;   // b = 20 
  printf(" b = %d ", b); 
  getchar(); 
  return 0; 
} 

Putting a bracket with comma makes b = a (or 10).

#include<stdio.h> 
int main() 
{ 
  int a = 10, b; 
  b = (20, a); // b = a 
  printf(" b = %d ", b); 
  getchar(); 
  return 0; 
} 

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