ideally don't use the String class and stick to cString (null terminated char arrays)
there are C libraries you can use to do many things on those defined in stdlib.h and string.h.
Here is an example using strtok() and atol()
char msg[] = "1,20,300,4000,50000";
void setup()
{
Serial.begin(115200);
Serial.print(F("Parsing String: "));
Serial.println(msg);
char* ptr = strtok(msg, ",");
byte i = 0;
Serial.println(F("index\ttext\tNumeric Value"));
while (ptr) {
Serial.print(i);
Serial.print(F("\t\""));
Serial.print(ptr); // this is the ASCII text we want to transform into an integer
Serial.print(F("\"\t"));
Serial.println(atol(ptr)); // atol(ptr) will be your long int you could store in your array at position i. atol() info at http://www.cplusplus.com/reference/cstdlib/atol
ptr = strtok(NULL, ",");
i++;
}
}
void loop() {}
You'll see in the console (set at 115200 bauds)
[color=purple]Parsing String: 1,20,300,4000,50000
index text Numeric Value
0 "1" 1
1 "20" 20
2 "300" 300
3 "4000" 4000
4 "50000" 50000
[/color]
PS: careful for the examples given above by other posters, the use of type uint8_t Ary[5];will limit number representation between 0 and 255. The parsing code does not detect any error and so if you have 1000 you'll overflow and won't get the right representation and if the number starts with a negative sign character it won't work either. If your array contains only small positive numbers fitting in a byte, then you are fine.
My code uses a library function to parse an long int, it can be positive or negative. Of course that code will fail if the input is not a number representation or does not fit in an unsigned long.