Why does printf(“value: %f”,10/2); output 0.000000?

Question

我知道整数算术将截断分数，但在这里它至少应打印5。为什么打印0.000000 ？

Answer 1

The call of printf has undefined behavior because the conversion specifier %f does not correspond to the type of the expression 10 / 2 , which is int . As the two operands of the expression 10 / 2 have the type int , the result has the type int because it is the common type of the both operands.

Use instead at least 10.0 / 2 . In this case, the expression has the type double .

Or output the integer expression 10 /2 using conversion specifier %d or %i like

printf( "value: %d", 10 / 2 );

From the C Standard (7.21.6.1 The fprintf function)

9 If a conversion specification is invalid, the behavior is undefined.275) If any argument is not the correct type for the corresponding conversion specification, the behavior is undefined .

Answer 2

10 and 2 aren't valid float s. They are int s.

To have your program print correct output, do this:

printf("value:%f",10./2.);

Notice the . after each number. This signifies to the compiler that the number is a floating-point number.