C struct glitch? (I am new to programing in C)

Question

I am learning how to create struct's and I am stuck on a program I made. Everything works fine until I try to input "2". When the program prints the symbol it's supposed to be "He" but prints "HeHelium" instead. I can't figure out what's wrong and why it's printing he.symbol and he.name all in one line. Link to image below.

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

struct Element {
    int num;
    double mass;
    char symbol[2];
    char name[20];
};


int main()
{
    struct Element h;
    h.num = 1;
    h.mass = 1.008;
    strcpy(h.symbol, "H");
    strcpy(h.name, "Hydrogen");

    struct Element he;
    he.num = 2;
    he.mass = 4.0026;
    strcpy(he.symbol, "He");
    strcpy(he.name, "Helium");

    int number;

    printf("Please enter the number of the element you want info on. \n");
    scanf("%d", &number);

    if (number == 1 /*&& !(number > 1)*/) {
        printf("Atomic Number: %d \n", h.num);
        printf("Atomic Mass: %.3f \n", h.mass);
        printf("Atomic Symbol: %s \n", h.symbol);
        printf("Atomic Name: %s \n", h.name);
    } else if (number == 2) {
        printf("Atomic Number: %d \n", he.num);
        printf("Atomic Mass: %.3f \n", he.mass);
        printf("Atomic Symbol: %s \n", he.symbol);
        printf("Atomic Name: %s \n", he.name);
    } else {
        printf("Invalid number! \n");
        printf("Or that element hasn't been added to the date base yet. \n");
        printf("Try back later \n");
    }

    return 0;
}

When I input "2": When I input 2

symbol[2] is too short, you forgot to account for the string null terminator. — Mat
– Mat, Commented Jan 19, 2021 at 21:32
symbol isn't big enough to hold "He", which requires three chars (two for the string data, and one for the terminator). With that, your program invokes undefined behavior. — WhozCraig
– WhozCraig, Commented Jan 19, 2021 at 21:33
After fixing the length, a more concise way to make the definition is struct Element he = { 2, 4.0026, "He", "Helium" }; or even better, make an array of struct indexed by the number. — Weather Vane
– Weather Vane, Commented Jan 19, 2021 at 21:38
Side note: In your switch, you are replicating the printf for hydrogen and helium. Better to move the printf to a "display" function that takes a const struct Element * as an argument and have each case call it (e.g.) display(&h); and display(&he); This would be more obvious if (e.g.) you had to print all 92 elements. — Craig Estey
– Craig Estey, Commented Jan 19, 2021 at 21:48

Miraz · Accepted Answer · 2021-01-20 15:36:19Z

You have assigned Element.symbol with only 2byte which can only store string with only one character as the other character will be used for null character. You should write "symbol[3]" as the symbol of elements in periodic table are no longer than 2 characters. Also, your code can become quite messy if you want to assign values for all 118 elements. You can write your code like below:

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

struct Elements {
    int num;
    double mass;
    char symbol[3];
    char name[20];
};

void print(struct Elements element)
{
    printf("Atomic Number: %d \n", element.num);
    printf("Atomic Mass: %.3f \n", element.mass);
    printf("Atomic Symbol: %s \n", element.symbol);
    printf("Atomic Name: %s \n", element.name);
}

void assignElement(struct Elements *givenElement, int num, float mass, char symbol[3], 
char name[20])
{
    givenElement->num=num;
    givenElement->mass=mass;
    strcpy(givenElement->symbol,symbol);
    strcpy(givenElement->name,name);
}

int main()
{
    struct Elements element[119];
    assignElement(&element[1], 1, 1.008, "H", "Hydrogen");
    assignElement(&element[2], 2, 4.06, "He", "Helium");
    assignElement(&element[3], 3, 6.09, "Li", "Lithium");

    int number;

    printf("Please enter the number of the element you want info on. \n");
    scanf("%d", &number);

    if (number < 119 && number > 0) {
        print(element[number]);
    } 
    else {
        printf("Invalid number! \n");
        printf("Or that element hasn't been added to the date base yet. \n");
        printf("Try back later \n");
    }
    return 0;
}

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