Not sure why my program keeps prompting error when I try to close it?

Question

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

int add_even(int);
int add_odd(int);

int main() {
    int num, result_odd, result_even, even_count, odd_count;
    char name;

    printf("What is your name?\n");
    scanf("%s", &name);

    while (num != 0) {
        printf("Enter a number:\n");
        scanf("%d", &num);

        if (num % 2 == 1) {
            printf ("odd\n");
            odd_count++;
        } else
        if (num == 0) {
            printf("%s, the numbers you have entered are broken down as follows:\n",
                  name);
            result_even = add_even(num);
            printf("You entered %d even numbers with a total value of %d\n",
                   even_count, result_even);
            result_odd = add_odd(num);
            printf("You entered %d odd numbers with a total value of %d\n",
                   odd_count, result_odd);
        } else {
            printf("even\n");
            even_count++;
        }
    }
    return 0;
} 

int add_even(int num) {
    static int sum = 0;

    if (num % 2 != 0) {
        return 0;
    }

    sum += add_even(num);
    return sum;
}

int add_odd(int num) {
    static int sum = 0;

    if (num % 2 == 0) {
        return 0;
    }
    sum += add_odd(num);
    return sum;
}

Can anyone give me some insight as to what I did wrong exactly?

The point of the code is to get inputs from the user until they decide to stop by inputting 0. Separating the evens from the odd. Tell them how many even/odd they put and the total of all the even/odd numbers.

I understand how to separate the evens from the odds. I think my issue is with my function.

Answer 1

There are multiple problems in your code:

• scanf() causes undefined behavior when trying to store a string into a single character. Pass an array and specify a maximum length.

• you should check the return value of scanf(): if scanf() fails to convert the input according to the specification, the values are unmodified, thus uninitialized, and undefined behavior ensues. In your case, if 2 or more words are typed at the prompt for the name, scanf("%d",...) fails because non numeric input is pending, no further characters are read from stdin and num is not set.

• num is uninitialized in the first while (num != 0), causing undefined behavior.

• functions add_even() and add_odd() are only called for num == 0, never summing anything.

• functions add_even() and add_odd() should always return the sum and add the value of the argument num is it has the correct parity. They currently cause undefined behavior by calling themselves recursively indefinitely.
• odd_count and even_count are uninitialized, so the counts would be indeterminate and reading their invokes undefined behavior.

In spite of all the sources of undefined behavior mentioned above, the reason your program keeps prompting without expecting an answer if probably that you type more than one word for the name. Only a single word is converted for %s, leaving the rest as input for numbers, which repeatedly fails in the loop. These failures go unnoticed as you do not verify the return value of scanf().

Here is a corrected version:

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

int add_even(int);
int add_odd(int);

int main(void) {
    int num, result_odd, result_even, even_count = 0, odd_count = 0;
    char name[100];

    printf("What is your name? ");
    if (scanf("%99[^\n]", name) != 1)
        return 1;

    for (;;) {
        printf("Enter a number: ");
        if (scanf("%d", &num) != 1 || num == 0)
            break;

        if (num % 2 == 1) {
            printf("odd\n");
            odd_count++;
            add_odd(num);
        } else {
            printf("even\n");
            even_count++;
            add_even(num);
        }
        printf("%s, the numbers you have entered are broken down as follows:\n", name);
        result_even = add_even(0);
        printf("You entered %d even numbers with a total value of %d\n",
               even_count, result_even);
        result_odd = add_odd(0);
        printf("You entered %d odd numbers with a total value of %d\n",
               odd_count, result_odd);
    }
    return 0;
} 

int add_even(int num) {
    static int sum = 0;

    if (num % 2 == 0) {
        sum += num;
    }
    return sum;
}

int add_odd(int num) {
    static int sum = 0;

    if (num % 2 != 0) {
        sum += num;
    }
    return sum;
}

Answer 2

You declared:

char name;                       // One single letter, such as 'A', or 'M'

printf("What is your name?\n");  // Please enter a whole bunch of letters!
scanf("%s", &name);              // Not enough space to store the response!

---

What you really want is more like

char name[31];                   // Up to 30 letters, and an End-of-String marker

printf("What is your name?\n"); // Please enter a whole bunch of letters!
scanf("%s", name);              // name is the location to put all those letters
                                // (but not more than 30!)