Getting wrong output when adding elements in 2D Array

Question

I am studying C programming now, I am not getting correct output when I am adding two elements in array, i am expecting your help to know the issue.

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

int main(void) {
    int limit = 0, sum[limit][3];
    int a[limit][3];
    int b[limit][3];

    printf("Enter the size of arrays: \n");
    fflush(stdout);
    scanf("%d", &limit);
    printf("Enter the values of Array 1");
    fflush(stdout);
    for (int i = 0; i < limit; i++) {
        for (int j = 0; j < limit; j++) {
            scanf("%d", &a[i][j]);
        }
    }

    printf("Array 1: \n");
    fflush(stdout);
    for (int i = 0; i < limit; i++) {
        for (int j = 0; j < limit; j++) {
            printf("%d\t", a[i][j]);
        }
        printf("\n");
    }
    printf("Enter the values of Array 2");
    fflush(stdout);
    for (int i = 0; i < limit; i++) {
        for (int j = 0; j < limit; j++) {
            scanf("%d", &b[i][j]);
        }
    }
    printf("Array 2: \n");
    for (int i = 0; i < limit; i++) {
        for (int j = 0; j < limit; j++) {
            printf("%d\t", b[i][j]);
        }
        printf("\n");
    }
    for (int i = 0; i < limit; i++) {
        for (int j = 0; j < limit; j++) {
            sum[i][j]= a[i][j] + b[i][j];
        }
    }
    printf("Sum of 2 arrays: \n");
    for (int i = 0; i < limit; i++) {
        for (int j = 0; j < limit; j++) {
            printf("%d\t", sum[i][j]);
        }
        printf("\n");
    }

    return EXIT_SUCCESS;
}

Current output:

Enter the size of arrays:

Enter the values of Array 1

Array 1:

12  12  12  
12  12  12  
12  12  12

Enter the values of Array 2

Array 2:

11  11  11  
11  11  11  
11  11  11

Sum of 2 arrays:

22  22  22  
22  22  22  
22  22  22

The problem i found that the exact array i gave in code that doesn't workout. My expected output is:

23 23 23
23 23 23
23 23 23

If your 2nd dimension is constant "3", and you're looping over this 3 items limit times, no wonder something goes wrong. Additionally, no wonder something goes wrong when limit is 0 when your sizing your arrays. — tofro
– tofro, Commented Oct 7, 2020 at 8:13

anastaciu · Accepted Answer · 2020-10-07 22:17:02Z

3

In:

int limit = 0, sum[limit][3];
int a[limit][3];
int b[limit][3];

limit is 0, your arrays will be:

int sum [0][3];
int a[0][3];
int b[0][3];

They will have space for nothing.

You should declare your arrays only after the limit input.

Also note that the second dimension of the array is fixed at 3, in your inner for cycles, instead of using limit you should use that constant value, otherwise, if limit is 4 or more, your program will access the array outside its bounds, invoking undefined behavior.

edited Oct 7, 2020 at 22:17

answered Oct 7, 2020 at 8:13

anastaciu

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1 Comment

Enrique_Iglesias Over a year ago

Great! got expected output.

chqrlie · Accepted Answer · 2020-10-07 08:21:42Z

There are multiple problems:

the arrays are defined with a dimension set to 0:

  int limit = 0, sum[limit][3];
  int a[limit][3];
  int b[limit][3];

you should define the arrays after you read the value og limit.

the nested loops use an incorrect boundary test:

  for (int i = 0; i < limit; i++) {
      for (int j = 0; j < limit; j++) {

j should iterate from 0 to 3 excluded.

Here is a modified version:

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

int main(void) {
    int limit = 0;

    printf("Enter the size of arrays: \n");
    fflush(stdout);
    if (scanf("%d", &limit) != 1 || limit < 1)
        return 1;

    int sum[limit][3];
    int a[limit][3];
    int b[limit][3];

    printf("Enter the values of Array 1");
    fflush(stdout);
    for (int i = 0; i < limit; i++) {
        for (int j = 0; j < 3; j++) {
            scanf("%d", &a[i][j]);
        }
    }

    printf("Array 1: \n");
    fflush(stdout);
    for (int i = 0; i < limit; i++) {
        for (int j = 0; j < 3; j++) {
            printf("%d\t", a[i][j]);
        }
        printf("\n");
    }
    printf("Enter the values of Array 2");
    fflush(stdout);
    for (int i = 0; i < limit; i++) {
        for (int j = 0; j < 3; j++) {
            scanf("%d", &b[i][j]);
        }
    }
    printf("Array 2: \n");
    for (int i = 0; i < limit; i++) {
        for (int j = 0; j < 3; j++) {
            printf("%d\t", b[i][j]);
        }
        printf("\n");
    }
    for (int i = 0; i < limit; i++) {
        for (int j = 0; j < 3; j++) {
            sum[i][j] = a[i][j] + b[i][j];
        }
    }
    printf("Sum of 2 arrays: \n");
    for (int i = 0; i < limit; i++) {
        for (int j = 0; j < 3; j++) {
            printf("%d\t", sum[i][j]);
        }
        printf("\n");
    }

    return EXIT_SUCCESS;
}

Shubhangi Chaturvedi · Accepted Answer · 2020-10-07 09:27:15Z

1

In the inner nested loops,j should iterate till j(excluding it) not limit. Required nested loop should be like-

for (int i = 0; i < limit; i++) {
      for (int j = 0; j < 3; j++) {
.
.
}

Tip:Declare your array after getting the input/size of the array from the user.

answered Oct 7, 2020 at 9:27

Shubhangi Chaturvedi

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