Validar letra

#include <stdio.h>

int main()
{
    char c;
    printf("Insert the letter: ");
    scanf("%c", &c);
    if(c >= 'A' && c <= 'Z' || c >= 'a' && c <= 'z')
        printf("Letra");
    else
        printf("No es una letra");
    return 0;
}