“％d！ =％ld'n”是指此代码？

Question

I'm still a beginner at C, so I'm finding difficulty in understanding "%d! = %ld". I know that %d and %ld are respectively used for an integer and long, so "! =" is confusing me.

#include<stdio.h>
long factorial(int);
int main() {
  int n;
  long f;
  printf("Enter an non-negative integer: ");
  scanf("%d", &n);
  if (n < 0)
    printf("Negative integers are not allowed.\n");
  else {
    f = factorial(n);
    printf("%d! = %ld\n", n, f); //what does this mean?
  }
  return 0; }
long factorial(int n) {
  if (n == 0)
    return 1;
  else
    return(n * factorial(n-1)); }

Answer 1

This will print:

• %d , ie the decimal value of int n
• ! = ! = , ie the literal character sequence
• %ld , ie the decimal value of long f

Answer 2

%d and %ld are the formatting placeholders for int and long int in printf . The exclamation point is just the factorial symbol, as mentioned in the comment.

Answer 3

printf() allows you to print a string with variables inside of it. Let's say you have a variable i , containing an integer, 7.

printf("My variable is %d", i);

Will print

My variable is 7

to the console! That's because %d is how you tell printf(), "Hey, put an integer variable here!". The integer is then supplied as the next argument to the function. In your case, %d represents the integer n , and %ld represents the long integer f . Since f might be really big, we make it a long, which means more bytes are allocated to it internally on your computer. So for example, if we wanted to get the factorial of 5 and print it, we might do the following:

printf("Factorial of %d equals %ld\n", 5, factorial(5))
// this will print "Factorial of 5 is 120" then a newline

Oh, and \\n just means print a newline afterwords!

Answer 4

printf("%d! = %ld\n", n, f); //what does this mean?

%d - print an integer as a signed decimal number.

l - specifies that the argument is a long int or unsigned long int as appropriate. %ld then prints a long int or unsigned long int

The printed text will become something like

n! = f 

(factorial notation n! )