float and double both are used for floating point and (irrational and rational) numbers size of float is 4 bytes in c and range of +/- 3.4e +/- 38 (~7 digits) and for double : +/- 1.7e +/- 308 (~15 digits) 8bytes and long double 10bytes you can refer let us c by yeshvant kanetkar
example-float a, b, c;
a = 2.854;
b = 7;c = 1.5e-7;