Thread: Hello guys, I have a question regarding Arrays

Is it better to use
#define at the top or should I just use

Code:

int myarray[10]= { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }

The problem when I go this route is that I get "Array not initialized or to long" something along those lines.

Definitely better to #define.

Code:

// To increase the array size, I'd have to make three separate changes.
// Imagine what it's like when that value is used in several different
// functions, and/or throughout several different source files.

#include <stdio.h>

int main(void)
{
    int array[10];
    int i;

    for(i=0; i<10; i++)
        array[i] = i+1;

    for(i=0; i<10; i++)
        printf("%d\n",array[i]);

    return 0;
}

Code:

// To increase the array size, I just change one value - the #define

#include <stdio.h>

#define MAX_LEN 10

int main(void)
{
    int array[MAX_LEN];
    int i;

    for(i=0; i<MAX_LEN; i++)
        array[i] = i+1;

    for(i=0; i<MAX_LEN; i++)
        printf("%d\n",array[i]);

    return 0;
}

If you could post a snippet of code, along with the exact warning/error messages you're seeing, perhaps we can figure out the problem you're running into.

Originally Posted by Matticus

Definitely better to #define.

Code:

// To increase the array size, I'd have to make three separate changes.
// Imagine what it's like when that value is used in several different
// functions, and/or throughout several different source files.

#include <stdio.h>

int main(void)
{
    int array[10];
    int i;

    for(i=0; i<10; i++)
        array[i] = i+1;

    for(i=0; i<10; i++)
        printf("%d\n",array[i]);

    return 0;
}

Code:

// To increase the array size, I just change one value - the #define

#include <stdio.h>

#define MAX_LEN 10

int main(void)
{
    int array[MAX_LEN];
    int i;

    for(i=0; i<MAX_LEN; i++)
        array[i] = i+1;

    for(i=0; i<MAX_LEN; i++)
        printf("%d\n",array[i]);

    return 0;
}

If you could post a snippet of code, along with the exact warning/error messages you're seeing, perhaps we can figure out the problem you're running into.

Well this are the instructions to my assignment


I tried using the way my teacher notes showed which included

Code:

int array[10]= { 1, 2 ...}
int array[12]= { 1, 2 ... 12}

but that never work and then I found the define function and that solved my problem

Anyways this is my code.. The teacher said to use A, B, C as our integer names but I learned from here to use more meaningful names..hopefully I don't get knocked off points for using more then the 3 he said or for not using the names he asked for..

Code:

#include <stdio.h>
#define SIZE 10
#define SIZE1 12


int main()
{
    int i;
    int j;
    int array1;
    int array2;
    int myArray[SIZE];
    int myArray2[SIZE1];
    int intersection[SIZE];
    int match;
    for (i=0;i<SIZE;i++)
    {
        printf("Enter number: ");
        scanf("%d",&myArray[i]);
    }
            for(i=0;i<SIZE;i++)
            {


            printf("%d\n",myArray[i]);
            }
    for (i=0;i<SIZE1;i++)
    {
        printf("Enter number: ");
        scanf("%d",&myArray2[i]);
    }
            for(i=0;i<SIZE1;i++)
            {
            printf("%d\n",myArray2[i]);
            }
    match = 0;
for(i=0; i<12; i++)
{
    for(j=0; j<12; j++)
    {
        if (myArray[i] == myArray2[j])
        {
            intersection[match] = myArray[i];
            match++;
        }


    }
}


    if (match>0)
    {
        printf("The intersection is: ");
        for(j=0; j<match; j++)
        printf("%d ",intersection[j]);
    }
    else
        printf("There is no intersection\n");
    return 0;
}

I also just realized I didn't use counter...damn.

Oh and here is to proof that it works

Also I have a very, very nooby question, I tend to think that my indentation is not the best. How do you guys indent one the source code starts to get huge?

Originally Posted by Cdd101

Also I have a very, very nooby question, I tend to think that my indentation is not the best. How do you guys indent one the source code starts to get huge?

I'm working on a reply to your previous post - I mention indentation.

Simple rule of thumb: every time you have code after an open brace '{', advance one tab stop. Every time you have a closing brace '}', go back one tab stop. Sometimes braces are optional - in that case, every time you have a line of code that depends on a control statement above it, indent that line of code.

Code:

//----------------
if(x == y)
{
    code 1;    // indent one level (underneath "if")
    code 2;    // indent one level (underneath "if")
}

//----------------
if(a == b)
    code 1;    // indent one level (underneath "if")

//----------------
for(i=0; i<10; i++)
{
    code 1;     // indent one level (underneath "for")
    code 2;     // indent one level (underneath "for")
    if(i < 6)   // indent one level (underneath "for")
        code 3;     // indent two levels (underneath "if", which is underneath "for")
    code 4;     // indent one level (underneath "for")
}

This might not be applicable for every situation, but it's a good method to generally follow.

More here: SourceForge.net: Indentation - cpwiki

The teacher said to use A, B, C as our integer names but I learned from here to use more meaningful names

This makes me very happy.

I made a few notes for you, and fixed the indentation - notice how it's easier to follow with the eyes.

Code:

#include <stdio.h>
#define SIZE 10
#define SIZE1 12

int main()
{
    int i;
    int j;
    int array1;
    int array2;
    int myArray[SIZE];
    int myArray2[SIZE1];
    int intersection[SIZE];
    int match;

    for (i=0;i<SIZE;i++)
    {
        printf("Enter number: ");
        scanf("%d",&myArray[i]);
    }

    for(i=0;i<SIZE;i++)
    {
        printf("%d\n",myArray[i]);
    }

    for (i=0;i<SIZE1;i++)
    {
        printf("Enter number: ");
        scanf("%d",&myArray2[i]);
    }

    for(i=0;i<SIZE1;i++)
    {
        printf("%d\n",myArray2[i]);
    }

    match = 0;

    // Instead of the "magic number" 12, you should use your defined constant SIZE here.
    // Moreover, "i" controls "myArray", which only has 10 elements, so by using 12,
    // you're overrunning the bounds of your array
    for(i=0; i<12; i++)
    {
        // and here, you should be using SIZE1 instead of the magic number 12
        for(j=0; j<12; j++)
        {
            if (myArray[i] == myArray2[j])
            {
                intersection[match] = myArray[i];
                match++;
            }
        }
    }

    if (match>0)
    {
        printf("The intersection is: ");
        for(j=0; j<match; j++)
        printf("%d ",intersection[j]);
    }
    else
        printf("There is no intersection\n");

    return 0;
}

There is one criteria of the assignment that is missing: "Repeated elements need to be counted only once. To do so, always check in C if the element to be inserted is already present."

Code:

Enter number: 1
Enter number: 2
Enter number: 3
Enter number: 4
Enter number: 5
Enter number: 6
Enter number: 7
Enter number: 8
Enter number: 9
Enter number: 10
1
2
3
4
5
6
7
8
9
10
Enter number: 1
Enter number: 2
Enter number: 2
Enter number: 2
Enter number: 2
Enter number: 2
Enter number: 2
Enter number: 2
Enter number: 2
Enter number: 2
Enter number: 2
Enter number: 2
1
2
2
2
2
2
2
2
2
2
2
2
The intersection is: 1 2 2 2 2 2 2 2 2 2 2 2 2

Well I did some changes on my code simply since I found some dead weight int on it.

Code:

	
Code:
	
#include <stdio.h>#define SIZE 10
#define SIZE1 12


int main()
{
    int i;
    int j;
    int A[SIZE];
    int B[SIZE1];
    int intersection[SIZE];
    int counter=0;


    for (i=0;i<SIZE;i++)
    {
        printf("Enter number: ");
        scanf("%d",&A[i]);
    }
            for(i=0;i<SIZE;i++)
            {


            printf("%d\n",A[i]);
            }
    for (i=0;i<SIZE1;i++)
    {
        printf("Enter number: ");
        scanf("%d",&B[i]);
    }
            for(i=0;i<SIZE1;i++)
            {
            printf("%d\n",B[i]);
            }


    for(i=0; i<12; i++)
    {
        for(j=0; j<12; j++)
        {
            if (A[i] == B[j])
            {
                intersection[counter] = A[i];
                counter++;
            }
        }
    }
    if (counter>0)
        {
            printf("The intersection is: ");
        for(j=0; j<counter; j++)
            printf("%d ",intersection[j]);
        }
    else
        printf("There is no intersection\n");
    return 0;
}

like

Code:

int array1
int array2

Also regarding matrixes, which is what my next assignment is over. Are there any recommended reads over that? I tend to not be able to understand my teachers notes very well.

Originally Posted by Matticus

This makes me very happy.

I made a few notes for you, and fixed the indentation - notice how it's easier to follow with the eyes.

Code:

#include <stdio.h>
#define SIZE 10
#define SIZE1 12

int main()
{
    int i;
    int j;
    int array1;
    int array2;
    int myArray[SIZE];
    int myArray2[SIZE1];
    int intersection[SIZE];
    int match;

    for (i=0;i<SIZE;i++)
    {
        printf("Enter number: ");
        scanf("%d",&myArray[i]);
    }

    for(i=0;i<SIZE;i++)
    {
        printf("%d\n",myArray[i]);
    }

    for (i=0;i<SIZE1;i++)
    {
        printf("Enter number: ");
        scanf("%d",&myArray2[i]);
    }

    for(i=0;i<SIZE1;i++)
    {
        printf("%d\n",myArray2[i]);
    }

    match = 0;

    // Instead of the "magic number" 12, you should use your defined constant SIZE here.
    // Moreover, "i" controls "myArray", which only has 10 elements, so by using 12,
    // you're overrunning the bounds of your array
    for(i=0; i<12; i++)
    {
        // and here, you should be using SIZE1 instead of the magic number 12
        for(j=0; j<12; j++)
        {
            if (myArray[i] == myArray2[j])
            {
                intersection[match] = myArray[i];
                match++;
            }
        }
    }

    if (match>0)
    {
        printf("The intersection is: ");
        for(j=0; j<match; j++)
        printf("%d ",intersection[j]);
    }
    else
        printf("There is no intersection\n");

    return 0;
}

There is one criteria of the assignment that is missing: "Repeated elements need to be counted only once. To do so, always check in C if the element to be inserted is already present."

Code:

Enter number: 1
Enter number: 2
Enter number: 3
Enter number: 4
Enter number: 5
Enter number: 6
Enter number: 7
Enter number: 8
Enter number: 9
Enter number: 10
1
2
3
4
5
6
7
8
9
10
Enter number: 1
Enter number: 2
Enter number: 2
Enter number: 2
Enter number: 2
Enter number: 2
Enter number: 2
Enter number: 2
Enter number: 2
Enter number: 2
Enter number: 2
Enter number: 2
1
2
2
2
2
2
2
2
2
2
2
2
The intersection is: 1 2 2 2 2 2 2 2 2 2 2 2 2

Thanks pal! So I did the changes to the names simply because the teacher is very picky regarding the naming. He wants us to use what he says so I tend to use real names or more useful names until it's time to turn it in.

Code:

#include <stdio.h>#define SIZE 10
#define SIZE1 12


int main()
{
    int i;
    int j;
    int A[SIZE];
    int B[SIZE1];
    int intersection[SIZE];
    int counter=0;


    for (i=0;i<SIZE;i++)
    {
        printf("Enter number: ");
        scanf("%d",&A[i]);
    }
            for(i=0;i<SIZE;i++)
            {


            printf("%d\n",A[i]);
            }
    for (i=0;i<SIZE1;i++)
    {
        printf("Enter number: ");
        scanf("%d",&B[i]);
    }
            for(i=0;i<SIZE1;i++)
            {
            printf("%d\n",B[i]);
            }


    for(i=0; i<SIZE; i++)
    {
        for(j=0; j<SIZE1; j++)
        {
            if (A[i] == B[j])
            {
                intersection[counter] = A[i];
                counter++;
            }
        }
    }
    if (counter>0)
        {
            printf("The intersection is: ");
        for(j=0; j<counter; j++)
            printf("%d ",intersection[j]);
        }
    else
        printf("There is no intersection\n");
    return 0;
}

Is that the only change you guys feel I should do to my assignment? I tend to ask questions on here a lot and this time I was determined to finish the assignment before asking on here.

Originally Posted by stahta01

Read up on Multiple or Two Dimension arrays.

Tim S.

Thank you so much for your help pal.

Huh after I change I did, using Size and Size 1 it now crashes at the end.

You can use:

Code:

#define ARRAYSIZE(array) (sizeof(array) / sizeof(array[0]))

It will work in the scope of where the array was defined.