converting string to number

let's say i have:
int x, y;

from the command line, say the user types "program -w -t -y 566 -o 123 -p" how can i get x = 566 and y = 123 ?

Code:

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int atoi (const char *string);

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thanks so much. didn't know that function existed in C..... i started with C++, maybe i should've started with C first... =)