NSString *string = [[NSString alloc]init];

for (int i = 0; i < 32; i++) {

int number = arc4random() % 36;

if (number < 10) {

int figure = arc4random() % 10;

NSString *tempString = [NSString stringWithFormat:@"%d", figure];

string = [string stringByAppendingString:tempString];

}else {

int figure = (arc4random() % 26) + 97;

char character = figure;

NSString *tempString = [NSString stringWithFormat:@"%c", character];

string = [string stringByAppendingString:tempString];

}

}

NSLog(@"%@", string);