variables - What is the difference between %g and %f in C?

Question

I was going through The C programming Language by K&R. Here in a statement to print a double variable it is written

printf("%g
", sum += atof(line));

where sum is declared as double. Can anybody please help me out when to use %g in case of double or in case of float and whats the difference between %g and %f.

Answer 1

They are both examples of floating point input/output.

%g and %G are simplifiers of the scientific notation floats %e and %E.

%g will take a number that could be represented as %f (a simple float or double) or %e (scientific notation) and return it as the shorter of the two.

The output of your print statement will depend on the value of sum.