Counting Uppercase & Lowercase in C

#include<stdio.h>

int main()
{
    char    ch[100];
    int lc=0, uc=0;
    int i;

    printf("Enter a string: ");
    gets(ch);

    for(i=0; ch[i]!=NULL; i++)
    {

        if(ch[i]>='A' && ch[i]<='Z')
            uc++;
        else if(ch[i]>='a' && ch[i]<='z')
            lc++;
    }

    printf("Upper case =  %d \n", uc);
    printf("Lower Case =  %d", lc);

    return 0;
}