银行卡卡号判断

- (BOOL) checkCardNo:(NSString*) cardNo{
    int oddsum = 0;     //奇数求和
    int evensum = 0;    //偶数求和
    int allsum = 0;
    int cardNoLength = (int)[cardNo length];
    int lastNum = [[cardNo substringFromIndex:cardNoLength-1] intValue];
    
    cardNo = [cardNo substringToIndex:cardNoLength - 1];
    for (int i = cardNoLength -1 ; i>=1;i--) {
        NSString *tmpString = [cardNo substringWithRange:NSMakeRange(i-1, 1)];
        int tmpVal = [tmpString intValue];
        if (cardNoLength % 2 ==1 ) {
            if((i % 2) == 0){
                tmpVal *= 2;
                if(tmpVal>=10)
                    tmpVal -= 9;
                evensum += tmpVal;
            }else{
                oddsum += tmpVal;
            }
        }else{
            if((i % 2) == 1){
                tmpVal *= 2;
                if(tmpVal>=10)
                    tmpVal -= 9;
                evensum += tmpVal;
            }else{
                oddsum += tmpVal;
            }
        }
    }
    
    allsum = oddsum + evensum;
    allsum += lastNum;
    if((allsum % 10) == 0)
        return YES;
    else
        return NO;
}