/*
we ask our user to enter a valid integer
and we output the square of the integer
*/
#include <stdio.h>
#include <stdlib.h>

int main()
{
    int inputInteger; //used to store user input
    int  inputSquared;// used to store the square of a valid integer.

    printf("Enter an Integer value....\n");
    scanf("\n%d",&inputInteger);//get input from user

    printf("You entered : %d\n", inputInteger);

    inputSquared = inputInteger*inputInteger;//find square
    printf("\n%d squared is %d\n",inputInteger, inputSquared);
    printf("\nSuccess!  Exiting program\n");

    return 0;
}

/*
this program shows how to validate user input as integers.
if the user enters a valid integer, we output the square of the integer,
otherwise we output an error message and prompt the user to re enter  a valid integer
*/
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h> //in order to use true and false

int main()
{
    char input[50]; //string used to store user input
    int  inputAsAnInteger;//used to store the converted input  as an integer
    int  inputSquared;// used to store the square of a valid integer.

    while(true)//loop 'infinitely'
    {
        printf("Enter an Integer value....\n");
        scanf("%s",&input);//get input from user

        printf("You entered : %s\n", input);

        inputAsAnInteger=atoi(input);//convert input to integer

        if (inputAsAnInteger==0)//if the input is not a number......
        {
            printf("Invalid input entered\n\n");
        }
        else//input is a number
        {

            inputSquared = inputAsAnInteger*inputAsAnInteger;//find square
            printf("\n%d squared is %d\n",inputAsAnInteger, inputSquared);
            printf("\nSuccess!  Exiting program\n");
            break;//exit 'infinite' loop.
        }
    }
    return 0;
}

/*
this program shows how to validate user input as integers.
if the user enters a valid integer, we output the square of the integer,
otherwise we output an error message and prompt the user to re enter  a valid integer
*/
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h> //in order to use true and false
#include <ctype.h>   // in order to use the isdigit function.

bool isNumber(char* stringArray);

int main()
{
    char input[50]; //string used to store user input
    int  inputAsAnInteger;//used to store the converted input  as an integer
    int  inputSquared;// used to store the square of a valid integer.

    while(true)//loop 'infinitely'
    {
        printf("Enter an Integer value....\n");
        scanf("%s",&input);//get input from user

        printf("You entered : %s\n", input);


        if (!isNumber(input))//if the input is not a number......
        {
            printf("Invalid input entered\n\n");
        }
        else//input is a number
        {
            inputAsAnInteger=atoi(input);//convert input to integer
            inputSquared = inputAsAnInteger*inputAsAnInteger;//find square
            printf("\n%d squared is %d\n",inputAsAnInteger, inputSquared);
            printf("\nSuccess!  Exiting program\n");
            break;//exit 'infinite' loop.
        }
    }
    return 0;
}

bool isNumber(char* stringArray)
{

    //go through each character
    //location in the array until
    //we reach the null character (end of input)
    for (int i = 0; stringArray[i]!='\000'; i++)
    {
        if(isdigit(stringArray[i])==0)//if the current character is not a digit....
            return false; //return false and end function here

    }

    return true;//return true since the entire array contained numeric characters
}

/*
this program shows an improved way to validate user input as integers.
it accepts negative numbers, and rejects text, numbers followed by text,
and numbers that are too big (or too small) to fit in an int.
if the user enters a valid integer, we output the square of the integer,
otherwise we output an error message and prompt the user to re-enter a valid integer
*/
#include <stdio.h>
#include <stdlib.h>  // in order to use the strtol function
#include <stdbool.h> // in order to use true and false
#include <string.h>  // in order to use the strchr and strcspn functions
#include <ctype.h>   // in order to use the isspace function
#include <errno.h>   // in order to use errno and ERANGE
#include <limits.h>  // in order to use INT_MIN and INT_MAX

bool toInteger(const char *text, int *result);

int main()
{
    char input[50]; //string used to store user input
    int  inputAsAnInteger;//used to store the converted input as an integer
    long long inputSquared;// used to store the square. long long, since the square of a big int does not fit in an int

    while(true)//loop 'infinitely'
    {
        printf("Enter an Integer value....\n");

        if (fgets(input, sizeof input, stdin) == NULL)//get a whole line from the user (at most 49 characters)
        {
            printf("No more input. Exiting program\n");
            return 1;
        }

        if (strchr(input, '\n') == NULL && !feof(stdin))//no newline means the line was too long to fit in input
        {
            int c;
            while ((c = getchar()) != '\n' && c != EOF)//throw away the rest of the line from the input buffer
                ;
            printf("Input too long\n\n");
            continue;//go back to the top of the loop and ask again
        }

        input[strcspn(input, "\n")] = '\0';//remove the newline that fgets keeps at the end

        printf("You entered : %s\n", input);

        if (!toInteger(input, &inputAsAnInteger))//if the input is not a valid integer......
        {
            printf("Invalid input entered\n\n");
        }
        else//input is a valid integer
        {
            inputSquared = (long long)inputAsAnInteger * inputAsAnInteger;//find square
            printf("\n%d squared is %lld\n", inputAsAnInteger, inputSquared);
            printf("\nSuccess!  Exiting program\n");
            break;//exit 'infinite' loop.
        }
    }
    return 0;
}

//tries to convert text to an int.
//returns true and stores the number in *result if the text is a valid int,
//otherwise returns false and leaves *result unchanged.
bool toInteger(const char *text, int *result)
{
    char *end;  //strtol points this at the first character it could not use
    long value; //strtol returns a long, which can hold bigger numbers than an int

    errno = 0;//clear any old error before calling strtol
    value = strtol(text, &end, 10);//convert the text to a base 10 number. Leading spaces and a + or - sign are allowed

    if (end == text)//no digits were found, e.g. "" or "abc"
        return false;

    if (errno == ERANGE || value < INT_MIN || value > INT_MAX)//the number is too big or too small for an int
        return false;

    while (isspace((unsigned char)*end))//skip any spaces after the number
        end++;

    if (*end != '\0')//something other than spaces was left over, e.g. "12abc"
        return false;

    *result = (int)value;//the text is a valid int, so store it
    return true;
}