Warning: array subscript has type char

Question

When I am running this program I am getting warning "array subscript has type 'char'". Please help me where is it going wrong. I am using code::blocks IDE

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
void NoFive()
{
    long long int cal;
    char alpha[25];
    char given[100] = "the quick brown fox jumped over the cow";
    int num[25];
    int i, k;
    char j;
    j = 'a';
    k = 26;
    cal = 1;
    for(i = 0; i <= 25; i++)
    {
        alpha[i] = j++;
        num[i] = k--;
      //  printf("%c = %d \n", alpha[i], num[i]);
    }
    for(i = 0; i <= (strlen(given) - 1); i++)
    {
        for(j = 0; j <= 25; j++)
        {
         if(given[i] == alpha[j]) ***//Warning array subscript has type char***
         {
            cal = cal * num [j]; ***//Warning array subscript has type char***
         }
         else
         {

         }
        }
    }
printf(" The value of cal is %I64u ", cal);
}

main()
{
NoFive();
}

Answer 1

Simple, change

char j;

to

unsigned char j;

or to just a plain (u)int

unsigned int j;
int j;

From GCC Warnings

-Wchar-subscripts Warn if an array subscript has type char. This is a common cause of error, as programmers often forget that this type is signed on some machines. This warning is enabled by -Wall.

The compiler doesn't want you to inadvertantly specify a negative array index. And hence the warning!