Thread: Reversing the order of the digits?

So far i have :

Code:

main(){
int num;
double s;
 int i=0;


printf("Enter 4 digit integer: ");
scanf("%d",&num);

s=sqrt(num);

printf("Square root of %d is: %6.4f \n", num, s);

but then i have to reverse num and print the square root of that reversed number. I'm lost. I know that I have to use char or array but i'm not even sure how to start.

Anybody can point me in the right direction?

Thanks

Or, you can scan it in as a string (character array), use strlen() to find out the actual length, and then just traverse the string one element at a time, copying the characters (digits) one at a time in reverse order to a new string.

Then use atoi() to convert the strings into integers to send to the sqrt() function.

strlen() is in <string.h>
atoi() is in <stdlib.h>

Look 'em up.

Originally posted by R.Stiltskin
Or, you can scan it in as a string (character array), use strlen() to find out the actual length, and then just traverse the string one element at a time, copying the characters (digits) one at a time in reverse order to a new string.

Then use atoi() to convert the strings into integers to send to the sqrt() function.

strlen() is in <string.h>
atoi() is in <stdlib.h>

Look 'em up.

I alredy know the lengh...it is always 4

all of that makes sense except traverse the string part...

to convert it to a charracter array:

Code:

char array_char[4]; 
sprintf(array_char,"%d",num);

but how would i traverse it?

I know after it would be easy..

Code:

int num2;
double ss;
num2 = atoi (reversed_char);
printf("Reversed number is:  %d \n", num2);
ss=sqrt(num2);
printf("Square root of %d is: %6.4f \n", num2, ss);

Here's a very simple example, inputting the number as a string to begin with. Of course, you can also do it your way, inputting it as an integer & then converting to a string. Either way the traversal would be similar. Note that the array length has to be 5 characters, terminating with the null character '\0'.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
                                                                                
int main(){
        char oldstr[5], newstr[5];
        int i;
        printf("Enter a 4-digit number > ");
        scanf("%s",&oldstr);
        printf("The number is %s.\n",oldstr);
        for(i=0;i<4;i++){
                newstr[i] = oldstr[3-i];
                newstr[4] = '\0';
        }
        printf("The new number is %s.\n",newstr);
                                                                                
return 0;
}

yay...i got it working

Code:

#include <stdio.h>

                                                                                
 main(){
        char digit[5];
		char reversdigit[5];
        int i;
		double s;
		double s2;
		int num;
		int reversnum;
        printf("Please enter a 4 integer : ");
        scanf("%s",&digit);
        printf("The number is %s.\n",digit);
       
		num= atoi(digit);
		s=sqrt(num);

	printf("The square root of %s is: %6.4f \n", digit, s);
		 
		  
		    for(i=0;i<4;i++){
                reversdigit[i] = digit[3-i];
                reversdigit[4] = '\0';
        }
        printf("The number in reverse is %s.\n",reversdigit);
		
			reversnum= atoi(reversdigit);
		s2=sqrt(reversnum);

	printf("The square root of %s is: %6.4f \n", reversdigit, s2);
                                                                                

}

it works but i still get an error
"warning: type mismatch in implicit declaration for built-in function `sqrt' " I understand why... converting int into double but it still works so i guess its okay.

BTW thanks for you help. I just started taking C at University. So i'm going to need a lot of help.


I did not like Java that much but looking back at it now Java looked a lot simpler.

Mak:
It works, but it complains because sqrt() wants a double as its argument. You can get rid of the error message by making the conversion explicit as in:

s = sqrt((double)reversnum);

This casts reversnum as a double before sending it to sqrt().


Zainny:
Right, & right.
Haste makes waste.

oh nice...#include <math.h> did the trick


Zainny, why do I have to use ??

Code:

int main() {
    /* code here */

    return 0;
}

even if it works without int and return 0; ?

Do i need it there so later on i could call that program from another program? Even though i would not do that but is that the logic behind it?




and here is the final program:

Code:

#include <stdio.h>
#include <math.h>

                                                                                
int main(){
        char digit[5];
		char reversdigit[5];
        int i;
		double s;
		double s2;
		int num;
		int reversnum;
        printf("Please enter a 4 integer : ");
        scanf("%s",digit);
        printf("The number is %s.\n",digit);
       
		num= atoi(digit);
		s = sqrt((double)num);

	printf("The square root of %s is: %6.4f \n", digit, s);
		 
		  
		    for(i=0;i<4;i++){
                reversdigit[i] = digit[3-i];
               
        }
		 reversdigit[4] = '\0';
        printf("The number in reverse is %s.\n",reversdigit);
		
			reversnum= atoi(reversdigit);
		s2 = sqrt((double)reversnum);;

	printf("The square root of %s is: %6.4f \n", reversdigit, s2);
                                                                                
return 0;
}

thanks again

hmm, can't you just reverse 4 digits with 2 loops and arrays, one counting up, one counting down? I have been reading your codes and it looks so difficult.

It could be also done this way I think:

Code:

#define N 4
int a[N], i;

    printf("Enter %d numbers: ", N);
    for (i=0;i<N;i++)
       scanf("%d", &a[i]);

    printf("In reverse order: ");
    for (i=N-1;i>=0;i--)
       printf("%d", a[i]);

It's much easier to understand.