I was going through The C programming Language by K&R. Here in a statement to print a double variable it is written
printf("\t%g\n", 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.
%f and %g does the same thing. Only difference is that %g is the shorter form of %f. That is the precision after decimal point is larger in %f compared to %g
E = exponent expression, simply means power(10, n) or 10 ^ n
F = fraction expression, default 6 digits precision
G = gerneral expression, somehow smart to show the number in a concise way (but really?)
See the below example,
The code
void main(int argc, char* argv[])
{
double a = 4.5;
printf("=>>>> below is the example for printf 4.5\n");
printf("%%e %e\n",a);
printf("%%f %f\n",a);
printf("%%g %g\n",a);
printf("%%E %E\n",a);
printf("%%F %F\n",a);
printf("%%G %G\n",a);
double b = 1.79e308;
printf("=>>>> below is the exbmple for printf 1.79*10^308\n");
printf("%%e %e\n",b);
printf("%%f %f\n",b);
printf("%%g %g\n",b);
printf("%%E %E\n",b);
printf("%%F %F\n",b);
printf("%%G %G\n",b);
double d = 2.25074e-308;
printf("=>>>> below is the example for printf 2.25074*10^-308\n");
printf("%%e %e\n",d);
printf("%%f %f\n",d);
printf("%%g %g\n",d);
printf("%%E %E\n",d);
printf("%%F %F\n",d);
printf("%%G %G\n",d);
}
The output
=>>>> below is the example for printf 4.5
%e 4.500000e+00
%f 4.500000
%g 4.5
%E 4.500000E+00
%F 4.500000
%G 4.5
=>>>> below is the exbmple for printf 1.79*10^308
%e 1.790000e+308
%f 178999999999999996376899522972626047077637637819240219954027593177370961667659291027329061638406108931437333529420935752785895444161234074984843178962619172326295244262722141766382622299223626438470088150218987997954747866198184686628013966119769261150988554952970462018533787926725176560021258785656871583744.000000
%g 1.79e+308
%E 1.790000E+308
%F 178999999999999996376899522972626047077637637819240219954027593177370961667659291027329061638406108931437333529420935752785895444161234074984843178962619172326295244262722141766382622299223626438470088150218987997954747866198184686628013966119769261150988554952970462018533787926725176560021258785656871583744.000000
%G 1.79E+308
=>>>> below is the example for printf 2.25074*10^-308
%e 2.250740e-308
%f 0.000000
%g 2.25074e-308
%E 2.250740E-308
%F 0.000000
%G 2.25074E-308
As Unwind points out f and g provide different default outputs.
Roughly speaking if you care more about the details of what comes after the decimal point I would do with f and if you want to scale for large numbers go with g. From some dusty memories f is very nice with small values if your printing tables of numbers as everything stays lined up but something like g is needed if you stand a change of your numbers getting large and your layout matters. e is more useful when your numbers tend to be very small or very large but never near ten.
An alternative is to specify the output format so that you get the same number of characters representing your number every time.
Sorry for the woolly answer but it is a subjective out put thing that only gets hard answers if the number of characters generated is important or the precision of the represented value.
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.
Source: Stackoverflow.com