string to int
int myInt = [myString intValue];
Source: Stackoverflow
int to string
NSString* myNewString = [NSString stringWithFormat:@"%d", myInt];
Source: Stackoverflow
C only
Because Objective-C with Cocoa don’t always answer the questions.
int i;
char * string = "1024";
i = atoi(string);
printf("%d", i);
Source: C Programming