Basic user input loop for numbers in range, modified to work with non numeric input and clear rubbish from stdin one of two ways.

hash_square.c

    #include <stdio.h>

    int clean_stdin()
    {
        while (getchar()!='\n');
        return 1;
    }  

    int main(void)
    {
        int lc1,lc2;/*loop count integers.*/
        int input=0;/*variable to hold the maximum count of rows/columns*/
        char temp[96];
        
        do
        {
            printf("Enter size of square [range 1:7]: ");
            if(scanf(" %i",&input)==1)
            {
                if ((input<1) || (input>7))
                    printf("The input must be in the range [1:7].\n");
            }
            else
            {
                printf("The input must be a whole number in the range [1:7].\n");
                scanf("%s", temp); /*either clear stdin with another scanf (not recommended)*/
                //clean_stdin(); /*or run special function to do it more reliably*/
            }
        } while ( (input<1) || (input>7) );
        
        printf("Input= %i\n", input);
        
        for (lc1=0;lc1<input;lc1++)
        {
            for (lc2=0;lc2<input;lc2++)
            {
                printf("#");
                if (lc2 < input-1)
                    printf("O");
            }
            if (lc1 < input-1)
                printf("\n");
        }
        
        return 0;
    }