为什么在if语句前后加“\n”就不会加空行？

Question

I attached some code below for my final output, I would like to have a full space between the entered values after -1 and the listing of the even and odd numbers. Thus far I have put printf("\n"); after the final if statement and before when they do not equal -1 . Any help would be appreciated

#include <stdio.h>

int main() {
    int input, numberEven, numberOdd;
    numberEven = 0;
    numberOdd = 0;
        
    do 
    {
        printf("Enter a value:");
        scanf("%d", &input);

        if (input != -1 && input % 2 == 0)
        {
            numberEven += 1;  
        }

        if (input != -1 && input % 2 != 0) 
        {
            numberOdd += 1;
        }
    }
    while (input != -1);
        
    printf("\nThe number of odd numbers is %d \n", numberOdd);
    printf("The number of even numbers is %d \n", numberEven);
    return 0;
}

Answer 1

Whether an empty line appears before The number of odd numbers is depends on the terminal:

• on linux and OS/X, reading from the terminal in cooked mode causes the terminal to echo user input after the prompt Enter a value: including the newline entered by the user, then the program outputs the string "\nThe number of odd numbers is...\n" starting with a newline, hence producing an empty line.
• on some legacy systems, such as Windows, user input is echoed but the newline seems missing and the next program output appears on the same line, but since you start with a newline, The number... appears on the next line without an intervening empty line.

The final newline in printf("The number of even numbers is %d \n", numberEven) causes the program output to end with a newline, so the command prompt appears on the next line on unix systems, but the behavior might be different on other systems. If you want a blank line after this output, add an extra \n at the end of the format line.

It is unclear what you mean by I have put printf("\n"); after the final if statement and before when they do not equal -1 . You should add an extra \n at the beginning of the format string if required.

Note that you should test the return value of scanf() to detect invalid input and premature end of file.

Note also that if the user inputs multiple values at the prompt, the behavior will be somewhat surprising but consistent as no further user input from the terminal is needed for the subsequent prompts:

chqrlie@linux:~/dev/stackoverflow$ gcc 220305-evenodd.c && ./a.out
Enter a value:1 2 3 4 5 -1
Enter a value:Enter a value:Enter a value:Enter a value:Enter a value:
The number of odd numbers is 3
The number of even numbers is 2
chqrlie@linux:~/dev/stackoverflow$