Explain an C expression with ? : and >

Question

Could anyone kindly explain me the use of a following expression in C?

double irate = argc > 1? atof(arg[1]) : 1;
double orate = argc > 2? atof(arg[2]) : 2;

(Taken from the beginning of an soxr example https://sourceforge.net/p/soxr/code/ci/master/tree/examples/1-single-block.c.)

Does it mean something like:

"if number of arguments is bigger than one, take the first argument and place it into the irate variable, otherwise put number 1 into the same variable"?

Similarly with the second possible argument...

atof() is just a libc conversion of a string (arguments are always treated as strings in Unix/Linux) to double, error (while conversion) handling is not provided.

Am I right?

Answer 1

double irate = argc > 1? atof(arg[1]) : 1;

Can be written as:

if (argc > 1)
    irate = atof(arg[1]);
else
    irate = 1

Or can be read as: if the argument count is greater than one, convert the second argument from an ascii string to a float and store it in the variable irate, otherwise set it to the value of 1.

Same for the second line.

Have a look at Conditional operator

Answer 2

irate and orate are supposed to be provided from command line, respectively as the first argument after the executable name (argv [1]) and as the second argument (argv [2]).

The expression

 double irate = argc > 1? atof(arg[1]) : 1;

is don to initialize the proper variable, but only if the corresponding argument has been provided. If not, the conversion would be meaningless, so a default value (1) is assigned.

The same can be said for orate: the default value 2 is assigned if the corresponding argument is not provided.