comma operator in if condition

Question

int a = 1, b = 0;

if(a, b)
   printf(\"success\\n\");
else
   printf(\"fail\\n\");

if(b, a)
   printf(\"success\\n\");
else
   printf(\"fail\");

Answer 1

Here is an example, provided by wikipedia, which shows another use case:

The comma can be used within a condition (of an if, while, do while, or for) to allow auxiliary computations, particularly calling a function and using the result, with block scoping:

if (y = f(x), y > x) { ... // statements involving x and y }

// See this Wikipedia discussion

Many C programmers have encountered the comma in the initializer part of a for statement, but not as many have seen it used in an if statement. In the case above it allows you to initialize y before the if statement tests the condition y>x.