格式化小数，四舍五入

//格式化小数 四舍五入类型
- (NSString *)decimalWithFormat:(NSString *)format double:(double)value
{
    NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init];

    [numberFormatter setPositiveFormat:format];

    return  [numberFormatter stringFromNumber:[NSNumber numberWithDouble:value]];
}