Basic While Loop Precedence (C)

Question

I'm new to coding and am learning C. I just had a question regarding while loops.

#include <stdio.h>

int main(void) {
    int integer1, integer2, number, sum, largest, smallest;
    float average;

    integer1 = 0;
    number = 0;
    sum = 0;
    largest = integer1;
    smallest = integer1;

    while (integer1 != -1) {
        printf("Enter the number: ");
        scanf_s("%d", &integer1);
        number++;
        sum = sum + integer1;

        if (integer1 >= largest) {
            largest = integer1;
        }
        if (integer1 <= smallest) {
            smallest = integer1;
        }
    }

    average = (float) sum / number;

    printf("The number of user's input: %d.\n", number);
    printf("The sum of input numbers: %d.\n", sum);
    printf("The average of input numbers: %.2f.\n", average);
    printf("The largest number is: %d.\n", largest);
    printf("The smallest number is %d.\n", smallest);

    return 0;
}

The objective of the code I've written is to:

Read integer values from the user.
Terminate the while loop when the user enters '-1'.
Output the printf statements with their corresponding values.

Here's the problem: All of the integer variables that I've declared should NOT include the value of '-1; inputted by the user. I assume that this has to do with an issue of precedence regarding the while loop, but I can't seem to pinpoint what it is. Any help or insight is greatly appreciated.

Thank you!

`smallest = integer1;` --> `#include ... smallest = INT_MAX;` — chux - Reinstate Monica, Mar 25 '17 at 13:14

score 4 · Accepted Answer · answered Mar 25 '17 at 11:17

Sometimes neither while nor do/while loop fit your needs, because the decision to exit the loop must be made in the middle of loop's body.

Reading values and deciding what to do after the read presents one of such situations. A common solution is to set up an infinite loop, and exit it from the middle on a break:

for (;;) {
    printf("Enter the number: ");
    scanf_s("%d", &integer1);
    if (integer1 == -1) {
        break;
    }
    ... // The rest of your code
}

Hari Lamichhane · Answer 2 · 2017-03-25T11:28:19.537

1

In order to achieve what you want you need to add one line.

 //use infinite loop
  while (1) {
        printf("Enter the number: ");
        scanf_s("%d", &integer1);
        //jump out of the loop because the loop has already started.
        //but the value was -1
        if (integer == -1) break;
        number++;
        sum = sum + integer1;

        if (integer1 >= largest) {
            largest = integer1;
        }
        if (integer1 <= smallest) {
            smallest = integer1;
        }
    }

edited Mar 25 '17 at 11:28

answered Mar 25 '17 at 11:16

Hari Lamichhane

520
5
11

Then the condition in the loop should probably be `while (true)` since you'll never hit the case where `integer` is -1 when checking the loop condition. – Michael Mior Mar 25 '17 at 11:21
Yes but in C you should use `while(1) { }` – Hari Lamichhane Mar 25 '17 at 11:27
That's a matter of opinion, but either one is preferable to the useless condition. – Michael Mior Mar 25 '17 at 11:29
1

@HariLamichhane [There was a whole Q&A on this topic](http://stackoverflow.com/a/20188551/335858), discussing `while (true)` vs `while (1)`. – Sergey Kalinichenko Mar 25 '17 at 11:39
@dasblinkenlight I was presuming he is not using `stdbool.h` i.e `true/false` is not available directly from `stdio.h` in C. Anyways thanks for the comment! – Hari Lamichhane Mar 25 '17 at 11:41
1

The biggest problem with all three options is that if you choose one somebody comes around and starts a discussion on it. There are many chances for wasting time. This is a classical one. It is the godfather of wasted time itself. – Amin Negm-Awad Mar 25 '17 at 11:57
great words @AminNegm-Awad. Thank you – Hari Lamichhane Mar 25 '17 at 11:58

score -1 · Answer 3 · answered Mar 25 '17 at 11:20

-1

Just add your scanf() statement prior to your while loop.

answered Mar 25 '17 at 11:20

Blessen George

270
3
18

Basic While Loop Precedence (C)

3 Answers3