just u follow following steps to convert c file to hex file
1.download and install keil compiler
2.open keil and project–>new project–>give name–> ok–>atmel–>89s52–>0k–>n0–>file–>new–> copy ur code here and save with .c extension–>right click on source group–>add files to source group and brouse ur file –>ok–>buildtarget–>right click on target–>options for target–>set freq 11.0592–>output–>select create hex file–>0k–>ok–>build target.
then u find hex file at ur project location.