What is the behavior of integer division?
CMathC99C89Integer DivisionC Problem Overview
For example,
int result;
result = 125/100;
or
result = 43/100;
Will result always be the floor of the division? What is the defined behavior?
C Solutions
Solution 1 - C
> Will result always be the floor of the division? What is the defined behavior?
Not quite. It rounds toward 0, rather than flooring.
> 6.5.5 Multiplicative operators
> 6 When integers are divided, the result of the / operator is the algebraic quotient with any fractional part discarded.88) If the quotient a/b is representable, the expression (a/b)*b + a%b shall equal a.
and the corresponding footnote:
> 88) This is often called ‘‘truncation toward zero’’.
Of course two points to note are:
> 3 The usual arithmetic conversions are performed on the operands.
and:
> 5 The result of the / operator is the > quotient from the division of the > first operand by the second; the > result of the % operator is the > remainder. In both operations, if the > value of the second operand is zero, > the behavior is undefined.
[Note: Emphasis mine]
Solution 2 - C
Dirkgently gives an excellent description of integer division in C99, but you should also know that in C89 integer division with a negative operand has an implementation-defined direction.
From the ANSI C draft (3.3.5): > If either operand is negative, whether the result of the / operator is the largest integer less than the algebraic quotient or the smallest integer greater than the algebraic quotient is implementation-defined, as is the sign of the result of the % operator. If the quotient a/b is representable, the expression (a/b)*b + a%b shall equal a.
So watch out with negative numbers when you are stuck with a C89 compiler.
It's a fun fact that C99 chose truncation towards zero because that was how FORTRAN did it. See this message on comp.std.c.
Solution 3 - C
Yes, the result is always truncated towards zero. It will round towards the smallest absolute value.
-5 / 2 = -2
5 / 2 = 2
For unsigned and non-negative signed values, this is the same as floor (rounding towards -Infinity).
Solution 4 - C
Where the result is negative, C truncates towards 0 rather than flooring - I learnt this reading about why Python integer division always floors here: Why Python's Integer Division Floors
Solution 5 - C
>Will result always be the floor of the division?
No. The result varies, but variation happens only for negative values.
> What is the defined behavior?
To make it clear floor rounds towards negative infinity,while integer division rounds towards zero (truncates)
For positive values they are the same
int integerDivisionResultPositive= 125/100;//= 1
double flooringResultPositive= floor(125.0/100.0);//=1.0
For negative value this is different
int integerDivisionResultNegative= -125/100;//=-1
double flooringResultNegative= floor(-125.0/100.0);//=-2.0
Solution 6 - C
I know people have answered your question but in layman terms:
5 / 2 = 2 //since both 5 and 2 are integers and integers division always truncates decimals
5.0 / 2 or 5 / 2.0 or 5.0 /2.0 = 2.5 //here either 5 or 2 or both has decimal hence the quotient you will get will be in decimal.