Reverse the order of an integer in C [closed] - c

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I am currently learning C as part of a course and I have a task to reverse the order of a number without using any arithmetic (wording of the task).
I currently have this:
#include <stdio.h>
int main()
{
int n, reverse = 0;
printf("Enter a number to reverse\n");
scanf("%d", &n);
while (n != 0) {
reverse = reverse * 10;
reverse = reverse + n_10;
n = n / 10;
}
printf("Reverse of entered number is = %d\n", reverse);
return 0;
}
But this solution uses arithmetic. How can I alter this to complete the task?
From the exercise sheet, "though even at three
digits the naïve approach quickly grows unmanageable with arithmetic (try it!).
Your goal: Design 3-digit solution without using any arithmetic.(Hint: use scanf.)"
The wording of the question was confusing but to be clear the question is:
How do you reverse the order of a number, e.g. 123456789 to 987654321, without without using math. So the solution is to scanf to read the number and swap the numbers in a loop as the answer below.

Answer 1

You can just read it in as a string.
int main()
{
char str[80];
fgets(str, 80, stdin);
strrev(str);
printf("%s\n", str);
}
void strrev(char *str)
{
char *end, tmp;
end = str + strlen(str) - 1;
for (; end > str; --end, ++str) {
tmp = *end;
*end = *str;
*str = tmp;
}
}
I don't know if you consider pointer arithmetic to be "arithmetic"

Answer 2

Read as series of short strings that can hold 1 digit and then print in the reserve order.
char buf[10][2] = { 0 };
scanf("%1[0-9]%1[0-9]%1[0-9]%1[0-9]%1[0-9]%1[0-9]%1[0-9]%1[0-9]%1[0-9]%1[0-9]",
&buf[0], &buf[1], &buf[2], &buf[3], &buf[4],
&buf[5], &buf[6], &buf[7], &buf[8], &buf[9]);
printf("%s%s%s%s%s%s%s%s%s%s",
buf[9], buf[8], buf[7], buf[6], buf[5],
buf[4], buf[3], buf[2], buf[1], buf[0]);
Obviously limited to max 10 digits.
A recusive approach, inpsired by #Nisse Engström. Works for any reasonable length input.
void pr(void) {
char digit[2];
if (scanf("%1[0-9]",digit)) {
pr();
printf("%s",digit);
}
}
int main(void) {
pr();
return 0;
}
Input
012345678901234567890123456789
Output
987654321098765432109876543210
Of course if (scanf("%1[0-9]",digit)) { should be if (scanf("%1[0-9]",digit) == 1) { to cope with EOF but that then may be "arithmetic".

Answer 3

Using scanf():
int
scanf (){
int
stdin =
getchar ();
return
stdin <0||
stdin ==
'\n'?
stdin :(
scanf (),
putchar (
stdin )),
'\n';}
int
main (){
putchar (
scanf ()
);}

Answer 4

Read integer, use sprintf() function to convert it into string and then use the library function strrev() to reverse the string.