iOS 数字 四舍五入 进一法 去尾法

四舍五入

1.整数

numberToRound = 4.51;
int result = (int)roundf(numberToRound);
NSLog(@"roundf(%f) = %d", numberToRound, result); 
// roundf(4.510000) = 5
numberToRound = 10.49;

result = (int)roundf(numberToRound);
NSLog(@"roundf(%f) = %d", numberToRound, result); 
// roundf(10.490000) = 10

numberToRound = -2.49;
result = (int)roundf(numberToRound);
NSLog(@"roundf(%f) = %d", numberToRound, result); 
//  roundf(-2.490000) = -2

numberToRound = -3.51;
result = (int)roundf(numberToRound);
NSLog(@"roundf(%f) = %d", numberToRound, result); 
// roundf(-3.510000) = -4

2.保留小数

CGFloat numberToRound = 4.51;
NSLog(@"%.1f",numberToRound);
//  4.5

进一法

1.整数

CGFloat numberToRound;
int result;
numberToRound = 4.51;
result = (int)ceilf(numberToRound);
NSLog(@"ceilf(%f) = %d", numberToRound, result);
// ceilf(4.510000) = 5

numberToRound = 10.49;
result = (int)ceilf(numberToRound);
NSLog(@"ceilf(%f) = %d", numberToRound, result);
// ceilf(10.490000) = 11

numberToRound = -2.49;
result = (int)ceilf(numberToRound);
NSLog(@"ceilf(%f) = %d", numberToRound, result);
// ceilf(-2.490000) = -2

numberToRound = -3.51;
result = (int)ceilf(numberToRound);
NSLog(@"ceilf(%f) = %d", numberToRound, result);
// ceilf(-3.510000) = -3

2.进一时保留小数

CGFloat numberToRound = 453210;
NSLog(@"%.1fW",ceil(numberToRound/1000.0)/10.f);
// 45.4W

去尾法

1.整数

int result;
CGFloat numberToRound = 4.51;
result = (int)floorf(numberToRound);
NSLog(@"floorf(%f) = %d", numberToRound, result);
// floorf(4.510000) = 4

numberToRound = 10.49;
result = (int)floorf(numberToRound);
NSLog(@"floorf(%f) = %d", numberToRound, result);
// floorf(10.490000) = 10

numberToRound = -2.49;
result = (int)floorf(numberToRound);
NSLog(@"floorf(%f) = %d", numberToRound, result);
// floorf(-2.490000) = -3

numberToRound = -3.51;
result = (int)floorf(numberToRound);
NSLog(@"floorf(%f) = %d", numberToRound, result);
// floorf(-3.510000) = -4

2.去尾时保留小数

  CGFloat numberToRound = 453210;
  // 保留一位
  NSLog(@"%.1fW",floorf(numberToRound/1000.0)/10.f);
  // 45.3W

  CGFloat numberToRound = 45.9210;
  // 保留两位小数点
  NSLog(@"%.2f",floorf(numberToRound*100.0)/100.f);
  // 45.92

这种方式比较简单，但是也很灵活多变，使用时需要多加注意。

oc方法

/**
 返回一个字符串，该字符串是进行格式化后的，格式化有三种，四舍五入，进一，去尾

 @param value 需要格式化的value
 @param position 保留的小数点
 @param roundingMode NSRoundPlain,四舍五入 NSRoundDown,去尾 NSRoundUp,进一
 @return 字符串
 */
+ (NSString*)stringWithRoundValue:(CGFloat)value
                       afterPoint:(NSUInteger)position
                     roundingMode:(NSRoundingMode)roundingMode {
  /*
   NSRoundPlain,   // 四舍五入
   NSRoundDown,    // 去尾
   NSRoundUp,      // 进一
  */
  NSDecimalNumberHandler* handler =
  [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:roundingMode
                                                         scale:position
                                              raiseOnExactness:NO
                                               raiseOnOverflow:NO
                                              raiseOnUnderflow:NO
                                           raiseOnDivideByZero:NO];
  NSDecimalNumber* ouncesDecimal;
  NSDecimalNumber* roundedOunces;
  
  ouncesDecimal = [[NSDecimalNumber alloc] initWithFloat:value];
  roundedOunces = [ouncesDecimal
                   decimalNumberByRoundingAccordingToBehavior:handler];
  return [NSString stringWithFormat:@"%@", roundedOunces];
}