C-Program to know the frequency of each character in sentence

#include<stdio.h>

#include<string.h>

int main()

{

    int i,k=0,count[26]={0},x;

    char str1[100];

    printf("Enter a sentence\n");

    gets(str1);   

    while(str1[k]!='\0')

    {

        if(str1[k]>='a'&&str1[k]<='z')

        {

            x=str1[k]-'a';

            count[x]++;

        }

        if(str1[k]>='A'&&str1[k]<='Z')

        {

           x=str1[k]-'A';

            count[x]++;

        }

        k++;

    }

    for(i=0;i<26;i++)

    {

        if(count[i]!=0)

        {

            printf("%c occured %d times\n",i+'a',count[i]);

        }      

    }

 return 0;

}