Can anyone explain the output

Question

If I try to print a float as an int , this code:

main () {                         
    float a = 6.8f;                      
    printf("%d", a);                      
}                       

prints 1073741824, while this code:

main () {            
    float a = 9.5f;           
    printf("%d", a);            
}                   

prints 0.

Is the output undefined? Also when is %f used with integer and %d used with double?

Answer 1

不仅输出，而且整个程序都有未定义的行为，因为传递给printf()的值的类型与格式字符串期望的类型不匹配。

Answer 2

From the C99 standard section 7.19.6.1 The fprintf function :

If any argument is not the correct type for the corresponding conversion specification, the behavior is undefined.

%d expects an int , not a float , so the program has undefined behaviour (including the output).

Answer 3

As described in previous answers if the print format doesn't match the type passed, it shows undefined behavior.

If you want to view integer as float u need to typecast it.

int j = 5;
printf("%f",(float)(j));

This will print output as 5.0 ie as a floating digit number

Answer 4

The C Standard says that the printf format must match the type passed in. If it doesn't, the behavior is expressly undefined:

C99, 7.19.6.1 # 9 (fprintf)

If a conversion specification is invalid, the behavior is undefined.239) If any argument is not the correct type for the corresponding conversion specification, the behavior is undefined.