How to check int or char in c

Question

I have a code where I convert celsius to fahrenheit. And I need to check what user writes char or int.

I've tried isalpha and isdigit, but they do not work.

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

int main()
{
    char t[] = "";
    scanf("%s", &t);
    if(isalpha(t))
    {
        printf("It's char\n");
    }
    else if (isdigit(t))
    {
        printf("It's int\n");
    }


    return 0;
}

Answer 1

isalpha and isdigit are applied to objects of the type int that contain a char.

You are trying to apply these functions to an object of the type char * (an array type is implicitly converted to a pointer type in expressions).

Moreover the array t declared like

char t[] = "";

is not enough large to store even one character gotten from scanf because it also need to store the terminating zero. Otherwise a call of scanf will have undefined behavior. And the call of scanf is also incorrect.

scanf("%s", &t);
            ^^^

It should be written at least like

scanf("%s", t);

You could declare an object of the type char like

char t;

and then use scanf like

scanf(" %c", &t);

and at last

if ( isalpha( ( unsigned char )t ) )
{
    printf("It's char\n");
}
else if ( isdigit( ( unsigned char )t ) )
{
    printf("It's int\n");
}