I have a variable of type char[] and I want to copy NSString value in it. How can I convert an NSString to a char array?
Use -[NSString UTF8String]:
NSString *s = @"Some string";
const char *c = [s UTF8String];
You could also use -[NSString cStringUsingEncoding:] if your string is encoded with something other than UTF-8.
Once you have the const char *, you can work with it similarly to an array of chars:
printf("%c\n", c[5]);
If you want to modify the string, make a copy:
char *cpy = calloc([s length]+1, 1);
strncpy(cpy, c, [s length]);
// Do stuff with cpy
free(cpy);