subs string case insentive

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

int main()
{

    char str1[100];
    char str2[100];

    gets(str1);
    scanf("%s", str2);

    int flag;
    for (int i = 0; str1[i] != '\0'; i++)
    {
        flag = 1;
        for (int j = 0; str2[j] != '\0'; j++)
        {
            if ('A' <= str1[i] && str1[i] <= 'Z')
            {
                str1[i] = str1[i] + 32;
            }

            if ('A' <= str2[j] && str2[j] <= 'Z')
            {
                str2[i] = str2[i] + 32;
            }
            if (str1[i] != str2[j])
            {
                flag = 0;
                break;
            }
            i++;
        }
        if (flag == 1)
        {
            break;
        }
    }

    if (flag == 1)
    {
        printf("Yes\n");
    }
    else
    {
        printf("No\n");
    }

    return 0;
}