How to merge two array

I want to merge the values of two arrays

For example

Code:

---

x = { 1, 2, 3, 4 }
y = { 3, 4, 5, 6, 7 }
z= {1, 2, 3, 4,3,4,5,6,7}

---

Code:

---

#include<stdio.h>

int main ()
{
    int i;
   
    int    x[] = { 1, 2, 3, 4 };
    int y[] = { 3, 4, 5, 6, 7 };
    int z[9];
   
    for (i = 0; i <4; i++)
    {
        &z[i];
    }


      for (i = 4; i <9; i++)
    {
        &z[i];
    }
       
    for (i = 0; i <9; i++)
    {
      printf("z[%d] = %d\n", i, z[i]);
 
    }
   
    return 0;
}

---

z[0] = 4199136
z[1] = 4199136
z[2] = 0
z[3] = 4200912
z[4] = 6422240
z[5] = 6422296
z[6] = 6422476
z[7] = 1979435552
z[8] = -1794567444

What's wrong with code ?

What do you think &z[i] is really doing? Hint it's not copying an array element from one array into another array.

Turn up the warning level.

Code:

---

$ gcc -Wall foo.c
foo.c: In function ‘main’:
foo.c:13:9: warning: statement with no effect [-Wunused-value]
        &z[i];
        ^
foo.c:19:9: warning: statement with no effect [-Wunused-value]
        &z[i];
        ^
foo.c:8:9: warning: unused variable ‘y’ [-Wunused-variable]
    int y[] = { 3, 4, 5, 6, 7 };
        ^
foo.c:7:12: warning: unused variable ‘x’ [-Wunused-variable]
    int    x[] = { 1, 2, 3, 4 };
            ^

---

Quote:

---

Originally Posted by Salem

Turn up the warning level.
[code]
$ gcc -Wall foo.c

---

I don't understand what i'm doing wrong

Code:

---

#include<stdio.h>
int main ()
{
    int i;
   
    int  x[] = { 1, 2, 3, 4 };
    int y[] = { 3, 4, 5, 6, 7 };
    int z[9];
   
    for (i = 0; i <4; i++)
    {
        z[i] = x[i];
    }
 
 
      for (i = 4; i <9; i++)
    {
        z[i] = y[i];
    }
       
    for (i = 0; i <9; i++)
    {
      printf("z[%d] = %d\n", i, z[i]);
 
    }
   
    return 0;
}

---

z[0] = 4199136
z[1] = 4199136
z[2] = 0
z[3] = 4200912
z[4] = 6422240
z[5] = 6422296
z[6] = 6422476
z[7] = 1979435552
z[8] = 2069808346

The problem is that when you append the second array, you need to start from index 0 for the second array, while starting from index 4 for the result array. Since you start from index 4 for both, you end up accessing the second array out of bounds.

Code:

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z[i] = y[i];

---

likely you want

Code:

---

z[i] = y[i-4];

---

Quote:

---

Originally Posted by laserlight

The problem is that when you append the second array, you need to start from index 0 for the second array, while starting from index 4 for the result array. Since you start from index 4 for both, you end up accessing the second array out of bounds.

---

I set index of second array to 0

Code:

---

#include<stdio.h>
int main ()
{
    int i;
   
    int  x[] = { 1, 2, 3, 4 };
    int y[] = { 3, 4, 5, 6, 7 };
    int z[9];
   
    for (i = 0; i <4; i++)
    {
        z[i] = x[i];
    }
 
 
      for (i = 0; i <9; i++)
    {
        z[i] = y[i-4];
    }
       
    for (i = 0; i <9; i++)
    {
      printf("z[%d] = %d\n", i, z[i]);
 
    }
   
    return 0;
}

---

z[0] = 4199136
z[1] = 4199136
z[2] = 0
z[3] = 4200912
z[4] = 6422240
z[5] = 6422296
z[6] = 6422476
z[7] = 1979435552
z[8] = -957751498

0-4 equals -4 and -4 is not a valid array index.

Quote:

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Originally Posted by stahta01

0-4 equals -4 and -4 is not a valid array index.

---

Well... it depends...

Code:

---

int a[4], *p = &a[2];
p[-2] = 0; // valid!. same as a[0].

---

I prefer to deal with pointers:

Code:

---

#define ARRAY_TEMS(a) (sizeof a / sizeof a[0])
int x[] = { 1, 2, 3, 4 };
int y[] = { 6, 7, 8, 9 10 };
int z[9]; // must have enough space to both x[] and y[] arrays.
int i;

int *p, *q;

q = z;

p = x;
for ( i = 0; i < ARRAY_ITEMS(x); i++)
  *q++ = *p++;

p = y;
for ( i = 0; i < ARRAY_ITEMS(y); i++)
  *q++ = *p++;

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

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Here is a solution that does not use pointers and gets to the heart of the issue, element positions are not the same in the second loop

Code:

---

/*Merge2Arraystoa3rd.c*/

#include<stdio.h>

int main ()
{
    int i;

    int x[] = { 1, 9, 3, 4 };
    int y[] = { 7, 2, 5, 8, 6 };
//    int z[9];
    int z[10]; // a C string must have one extra element for the "\0" //See Strings in C - GeeksforGeeks
    for (i = 0; i <4; i++)
    {
        //&z[i];
        z[i] = x[i]; // each element in array x will copy into the same array element position in z
    }                // but this is not the same in the next iteration

    for (i = 0; i <5; i++) // Element position 0 in y is equal to element position 4 in z
    {
        //&z[i];
        z[i+4] = y[i];
    }

    for (i = 0; i <9; i++)
    {
      printf("z[%d] = %d\n", i, z[i]);
    }
    return 0;
}[

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