Thread: problem with isdigit(), something causing segmentation fault

I've came up with my own idea for a program, just to test mysel. Unfortunately I did not succeed.
The idea is - accept input only if it is a number, return to scanf otherwise.
Here is the code, it is giving me segmentation fault, and I have no idea what is wrong...

Code:

#include <stdio.h> 
#include <stdlib.h> 
#include <ctype.h>


int main()
{
            int i ,j;
            char d;
            char input[20];
            int transformed[20];
                        
            printf("Please enter a number\n");
            scanf("%s", input);
            for (i = 0; i < 20; i++) {
            transformed[i] = atoi(input[i]);
            }
            do {
                for (j = 0; j <20; j++) {    
                    if (isdigit(transformed[j])) 
                    printf("Thanks for the number");
                    else {
                   printf("It is not a number. Please enter a number");
                        printf("Press r to repeat\n"); 
                    }
                }                   
            scanf("%c", &d);
            } while (d != 'r');
            return 0;                        
}

I appreciate Your help very much, however again it doesn't work properly. At least now, there's no segmentation fault

isdigit seems to be not detecting numbers, and even though I clear the buffer, there is no possiblity to enter char d, to decide if we want to finish the loop.

Code:

Code:

#include <stdio.h> 
#include <stdlib.h> 
#include <ctype.h>
#include <string.h>

int main()
{
            int i, j, found, yes;
            char d;
            char input[20];
            
            do {
                    printf("Please enter a number\n");
                    scanf("%s", input);
                    j = 0;
                    for (i = 0; i < 20; i++) {
                        if (isdigit(input[i]) == 1) {
                            j++;
                        }
                    }    
                    if(j == strlen(input))    
                        yes = 1;
                    if (yes == 1)
                        found = 1;
                    else 
                        found = 0;
                    if (found == 1) 
                    printf("Thanks for the number");
                    else {
                   printf("It is not a number. Please enter a number");
                        printf("Press r to repeat\n"); 
                    }
            fflush(stdin);
            scanf("%c", &d);
            } while (d != 'r');
            return 0;                        
}

Thanks in advance!

Check line 17. More on isdigit() here.

isdigit(2) = Returns a value different from zero (i.e., true).
isdigit(a) = Returns zero (i.e., false).

Double check what value is being returned by isdigit() with a printf statement.

Originally Posted by Click_here

I know that you are having trouble with input - use gets(input) instead of the scanf function and get rid of fflush(stdin) and use d=getchar();

Well don't use gets, either.

Well don't use gets, either.

Fair enough. I was just trying to help Pole get the code working - But to be complete, whiteflags is right.

If you don't follow that link, it suggests to use fgets due to the risk of buffer overrun.

If you are going to use fgets, look into ways of clearing/dealing with the input buffer on the event of too much input. This link gives you another explanation and how to use fgets and clearing the buffer on the event that your variable couldn't hold all the input IP Banned - GIDNetwork ("Things to avoid in C/C++ -- gets() Part 1")

Originally Posted by Click_here

If you are going to use fgets, look into ways of clearing/dealing with the input buffer on the event of too much input. This link gives you another explanation and how to use fgets and clearing the buffer on the event that your variable couldn't hold all the input IP Banned - GIDNetwork ("Things to avoid in C/C++ -- gets() Part 1")

I wouldn't recommend that code. It's just as bad as gets(). They strcat() a dummy array of 50 chars to a buffer array of 5 chars --> BOOM
But correctly implemented the idea wouldn't be bad.

Kurt

I wouldn't recommend that code. It's just as bad as gets(). They strcat() a dummy array of 50 chars to a buffer array of 5 chars --> BOOM
But correctly implemented the idea wouldn't be bad.

Kurt

I didn't see that strcat in there -> A dummy variable should be a dummy variable! (unhappy face)

Don't use that code.

If your input is too large for your array, you need to read all the inputs into a dummy array -> From there I'd disregard all input, display an error message (i.e. "input too large - needs to be less than 'x') and prompt for input again.