Garbage values in array display c++

Question

When I tried to execute this code am getting the garbage values in the output.

int empid;
int unit500[] = {3,5,6,7,8,9};
int unit1000[] = {4, 6, 7, 8, 9, 10};
int unit924[] = {10, 9, 8, 5, 4, 3};
cout << "Enter emp id: ";
cin >> empid;
if(empid == 2)
{
    cout << empid << endl;
}
else if(empid == 500)
{
    for(int i=0; unit500[i] != '\0'; i++)
    {
        cout << unit500[i];
    }
}
else if(empid == 1000)
{
    for(int j=0; unit1000[j] != '\0'; j++)
    {
        cout << unit1000[j];
    }
}
else if(empid == 924)
{
    for(int k=0; unit924[k] != '\0'; k++)
    {
        cout << unit924[k];
    }
}

Output:

Enter emp id: 500 35678950042012642293652942012642293584229365241989632147332096

how about looping from 0 to the array size & not till ur element is different from '\0"? — Spinkoo
– Spinkoo, Commented Jun 15, 2020 at 10:09

Fareanor · Accepted Answer · 2020-06-15 13:01:42Z

3

Why are you looking for a char inside an array of int ? (Well, this is not an error, I just wanted to point out a consistency mistake here)

Actually, the character '\0' is promoted to the integer 0. Since none of your arrays contain any 0, you'll get an infinite loop for each of your for loops.

But it is probably not the behaviour you was expecting. It seems that you want to display the whole array.
Note that a c++ array is not a C String so don't expect it to be null-terminated !
In this case, you just have to iterate until the size of the array is reached.

For example:

//...
int unit500[] = {3,5,6,7,8,9};

//...

// Get the size of unit500
const unsigned int unit500_size = sizeof(unit500) / sizeof(unit500[0]);

// Or (since C++17)
//const unsigned int unit500_size = std::size(unit500);

// Iterate until the last element of unit500
for(unsigned int i = 0; i < unit500_size; ++i)
{
    std::cout << unit500[i] << ", ";
}

//...

Of course, using std::array would be a better option. You could get the size in a significantly more readable way by simply calling the size() method.

edited Jun 15, 2020 at 13:01

answered Jun 15, 2020 at 10:21

Fareanor

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6 Comments

underscore_d Over a year ago

Agreed that std::array is preferable (at least until the languages fixes the shortcomings of 'native' arrays). However, if one 'must' use a 'native' array, std::size() handles that since C++17.

crsn Over a year ago

I like your answer :) I just wanted to point out that \0 is not implicitily converted. \0 IS the null character: open-std.org/JTC1/SC22/WG14/www/docs/n1124.pdf [page 61, example 12]

Fareanor Over a year ago

@underscore_d Oh right, I didn't think of it, I'll edit my answer accordingly. Thanks for the improvement :)

Fareanor Over a year ago

@crsn Thank you for the comment :) I know '\0' is the null character but we are considering here an array of int (and not char), so when the comparison occur, the char is promoted into an int (if I'm not mistaken). By the way, you linked a C documentation, not a C++ one (since they are two completely different languages you can't apply it to both languages, the rules differ a lot).

Fareanor Over a year ago

@crsn Yes, this is right, I just wanted to point out the semantic difference between '\0' as a char and 0 as an integer. Indeed the numeric values are exactly the same (0) but only the first one is called null character (hence the semantic distinction). But I will correct my answer which is indeed incorrectly stated :)

|

PhoenixBlue · Accepted Answer · 2020-06-15 10:12:59Z

0

Your condition to end the loop is not adequate. Rather use a counter, loop until the counter is equal to the size of the array

for(int i=0; i<6/*size of array*/; i++){
     ...
}

answered Jun 15, 2020 at 10:12

PhoenixBlue

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Comments

NixoN · Accepted Answer · 2020-06-15 10:14:26Z

You can fix it like this:

#include <iostream>
#include <vector>
int main()
{
    int empid;
    std::vector<int> unit500 = { 3,5,6,7,8,9 };
    std::vector<int> unit1000 = { 4, 6, 7, 8, 9, 10 };
    std::vector<int> unit924 = { 10, 9, 8, 5, 4, 3 };
    std::cout << "Enter emp id: ";
    std::cin >> empid;
    if (empid == 2)
    {
        std::cout << empid << std::endl;
    }
    else if (empid == 500)
    {
        for (int i = 0; i != unit500.size(); i++)
        {
            std::cout << unit500[i];
        }
    }
    else if (empid == 1000)
    {
        for (int j = 0; j != unit1000.size(); j++)
        {
            std::cout << unit1000[j];
        }
    }
    else if (empid == 924)
    {
        for (int k = 0; k != unit924.size(); k++)
        {
            std::cout << unit924[k];
        }
    }
}

Garbage value because there is no '\0' character in integer arrays. By the way it's easier to work with vector rather than with arrays.

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