what mean this " return x < 0 ? 2 - y : y;" in the end of function

[ranaphd]

Hi
please help me to depict what does mean this " return x < 0 ? 2 - y : y;" in the end of function.

the function is as follows:

double erfc(double x)
{
    double t, u, y;
 
    t = 3.97886080735226 / (fabs(x) + 3.97886080735226);
    u = t - 0.5;
    y = (((((((((0.00127109764952614092 * u + 1.19314022838340944e-4) * u - 
        0.003963850973605135) * u - 8.70779635317295828e-4) * u + 
        0.00773672528313526668) * u + 0.00383335126264887303) * u - 
        0.0127223813782122755) * u - 0.0133823644533460069) * u + 
        0.0161315329733252248) * u + 0.0390976845588484035) * u + 
        0.00249367200053503304;
    y = ((((((((((((y * u - 0.0838864557023001992) * u - 
        0.119463959964325415) * u + 0.0166207924969367356) * u + 
        0.357524274449531043) * u + 0.805276408752910567) * u + 
        1.18902982909273333) * u + 1.37040217682338167) * u + 
        1.31314653831023098) * u + 1.07925515155856677) * u + 
        0.774368199119538609) * u + 0.490165080585318424) * u + 
        0.275374741597376782) * t * exp(-x * x);
    return x < 0 ? 2 - y : y;
}

Thanks

[donbock]

return x < 0 ? 2-y : y;

is equivalent to

if (x < 0)
   a = 2-y;
else
   a = y;
return a;

x < 0 ? 2-y ? y is called a conditional expression.
The ? operator is called the ternary operator.

Personally, I don't find much use for the ternary operator in the code that I write.

[weaknessforcats]

The idea behind the ternary operator comes from the old days when computers had very little memory. Generally, the less code you write, the less instructions are generated by the compiler. The ternary operator was an attempt to generate the least amout of code in the executable.

And ditto, I don't use it either.