Hi Nabila,
Refer, to your datasheet when trying to understand about registers. Do refresh your memory regarding hexadecimal and binary.
[quote user="Nabila Naorin"]GPIO_PORTF_DEN_R = 0x14; // 7) enable digital I/O on PF4, pf2[/quote]
This is correct. Refer to GPIODEN register.
[quote user="Nabila Naorin"]GPIO_PORTF_DATA_R=0x04; // set pf4 to 1[/quote]
This sets PF2 to 1, not PF4. Refer to GPIODATA register
-kel