Difference

what is the difference between sformat & sformatf can any one explain with example

The difference is described in the free IEEE Std 1800-2012 in section 21.3.3 Formatting data to a string

$sformat is a system task whereas $sformatf is a function.

$sformat has 2 arguments(this interprets the second argument and stores formatted o/p string into the 1st argument).

$sformatf has a single argument whose result is stored into a separate variable as a return value.

module m1;
 string s;
 int a = 32;
 initial 
 begin
 $sformat(s, "\n formatf value of a = %0d\n", a);
 $display("%s", s);
 end
 
 initial 
 begin
   s = $sformatf("\n sformatf value of a = %0d \n", a);
   //$sformatf("\n sformatf value of a = %0d \n", a);
   $display("%s",s);
 end
endmodule

Basically these are used for formatting data into a string.