Compiler Warning (level 4) C4706

assignment used as a condition

The test value in a conditional expression is the result of an assignment.

An assignment has a value (the value on the left side of the assignment) that can be used legally in another expression, including a test expression.

The following sample generates C4706:

// compile with: /W4
int main()
{
   int a = 0, b = 0;
   if (a = b) // C4706
   {
   }
}

Suppress the warning with ((expression)). For example:

// compile with: /W4
int main()
{
   int a = 0, b = 0;
   if ((a = b)) // No warning
   {
   }
}

If your intention is to test a relation, not to make an assignment, use the == operator. For example, the following tests whether a and b are equal:

// compile with: /W4
int main()
{
   int a = 0, b = 0;
   if (a == b)
   {
   }
}

If you intend to make your test value the result of an assignment, test to ensure that the assignment is non-zero or non-null. For example, the following code doesn't generate this warning:

// compile with: /W4
int main()
{
   int a = 0, b = 0;
   if ((a = b) != 0)
   {
   }
}