Flash memory usually allow about 10'000 write operations. The EEPROM allows about 100'000 write cycles till it gets unreliable. An SD card has the same restrictions but there you have an intelligent controller on the card reordering the write operations in a way that the blocks written to change in every write operation. This way you can use an SD card more like a hard drive but the limitations still apply.

If your project includes an RTC use the nonvolatile RAM they offer because that memory area can be written as many times as you like.

yes i have RTC in my project to show date and time for each object but i can't  understand you in this point (

RTC use the nonvolatile RAM they offer because that memory area can be written as many times as you like

How use the nonvolatile RAM ?
i know RAM is volatile memory !

I make project counting object , I use eeprom to store data when reset board start counting from where i have left from the previous count
but i'm worry because i use it to store data 300 time in day ,I don't know if the repeating of store data in eeprom will make problem in long time because i read There is a limited number of write cycles available for eeprom and i want to know if it safe or not &
if i use SD card ,Is it better than eeprom or not ? & if SD card better ,How i save data with address ?

Thanks

but can i write at a particular memory location repeatedly?

You can. There is a limited number of write cycles available, but that number is greater than 100,000.

Why do you need to keep counting from the same value? Are you implementing some kind of hour-meter?

Please i need to save data when shudown the board and i use eeprom but i'm worry because i use it 300 time in day i don't know you mean we use it 100,000 for one register nor 100,000 for 256 (all register) and i want to know if it safe or not ,

, if i use SD card ,Is it better than eeprom or not ?
,if SD better ,How i save data with address ?
Thanks

schematic

I finished  hardware connections with two 74hc595 for one 8*8 led matrix , i need simple code to set cursor then print data into led matrix or clear it or any library can help me

i want to make LED screen using a lot of 8*8 led matrix  and i need to send data from arduino to show in it , i need simple code to show any letter on it , can i found library like lcd library,i need to use this matrix like lcd define the row and coulmn then send data will written and disappear if i clear it 

The buffer is your char array - often used word for the same thing.

 thanks  

Read each line from the file into a line buffer. When there is no more data in the file, what's left in the buffer is the last line.

sorry , but i don't know how Read each line from the file into a line buffer

As mentioned, working with an Excel file on the arduino would be challenging. For the text file though you can use the SD library's read function to build a function that reads your text file line by line into a (suitably sized) char array. Then you can use that to read until end of file, leaving the last line of the file in your buffer. Simply parse whatever data your interested in out of that. Don't forget to defend yourself against buffer overflow if it turns out that the lines in the file are longer than you thought and are too big for your char array.

Google should be able to find you a C function that reads a text file line by line if you don't want to write your own.

thanks for your answer , i can make array and save read data into it but i don't understand how i can leaving the last line of the file in your buffer
i don't know what buffer ?
 

Please , How i read the last data input on excel sheet or txt file

Did you want to program an Arduino to drive those particular 5x7 display modules or did you want to design your own 5x7 display modules?

Form the datasheet (http://www.electronics123.net/amazon/datasheet/MLD1_datasheet_v1.pdf) it looks like they are sing the SPI hardware to shift data out very quickly.  For each line of each module you shift out two bytes: one to select which column and one to light the rows in that column.

i want to design my own 5x7 display modules

i want to make LED screen display using led matrix 5*7 , i search for led matrix library but i can't found it , i need to make led screen like this ( http://www.electronics123.com/Programmable-5-x-7-Modular-LED-Matrix-Display.html ) without computer software interface ,
 i only need to show any const or variable  in the program like in the lcd display ( lcd.print("Hello world")

thanks

 can i communicate two device using the Serial Peripheral Interface (SPI) Bus in one arduino board ?
because i need to connect two device ( SD card shield with screen led matrix ) in one program and both of them need SPI pins , i don't know if one board include to two SPI pins or not and if not, How i connect two arduino board together work on the same program  ?

I don't understand what you mean by either of those questions.

i mean now i can save data on excel sheet in sd card i need to delete this data from excel  sheet using arduino board sush as lcd.clear  in LCD