The part before the first comma ('p%d=%.8f\n') looks like a format specifier, as would be used in sprintf or fprintf. It means: print a "p" followed by an integer followed by "=" followed by a floating-point number with 8 decimal places followed by a new-line character.
The i and c would be subsequent arguments so that i would be the integer printed and c would be the floating-point number.
For example:
i = 3;
c = 0.123;
sprintf('p%d=%.8f\n',i,c)
