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

#define BUFFERSIZE 10

int main() {

/* Width is the width of the diamond provided by user.
   Check is a pointer required by strtol() below */
        int width;
        char *check;

/* Allocate memory for input string */
        char *input = (char *)malloc(BUFFERSIZE+2);

/* Checks to see if malloc() succeeded */
        if(input == NULL) {
                printf("Error: Failed to allocate memory.\n");
                return 1;
        }

        printf("Enter an integer: ");

/* Reads input and checks to see if it's a string. fgets() is better
   than scanf(), which can result in buffer overflows.. */
if(fgets(input, BUFFERSIZE+2, stdin) == NULL) {
        printf("Error: No input given.\n");
        return 1;
}

/* Checks to see if input is a number. If so, converts it to an int */
        if(isNumber(input)) {
                width = strtol(input, &check, 0);
                if(width < 1) {
                        printf("Error: Input was not a positive integer.\n");
                        return 1;
                }
                printf("The width of the integer is %d.\n", width);
        } else {
                printf("Error: Input was not a positive integer.\n");
        }

/* Always deallocate memory, even if this is your entire program */
        free(input);
}

/* Returns 1 if input is an integer; returns 0 otherwise. */

int isNumber(char *input) {
        int i;
        for(i = 0; input[i] != '\0'; i++) {
                if(isalpha(input[i]))
                        return 0;
                else
                        return 1;
        }
}