C Program to Implement Variable Length Array

This is a C Program to implement variable length array(Vectors). An array (vector) is a common-place data type, used to hold and describe a collection of elements. These elements can be fetched at runtime by one or more indices (identifying keys). A distinguishing feature of an array compared to a list is that they allow for constant-time random access lookup, compared to the latters sequential access. Resizable arrays allow for an unspecified upper-bound of collection elements at runtime, and are conceptuality similar to a list. These dynamic arrays are more complicated and less used in introduction to its compatriot list, which is dynamic by nature. Using C as the language of implementation this post will guide you through building a simple vector data-structure. The structure will take advantage of a fixed-size array, with a counter invariant that keeps track of how many elements are currently present. If the underlying array becomes exhausted, the addition operation will re-allocate the contents to a larger size, by way of a copy.

Here is source code of the C Program to Implement Variable Length Array. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

```
#include <stdio.h>
```
```
#include <stdlib.h>
```
```
 
```
```
#ifndef VECTOR_H
```
```
#define VECTOR_H
```
```
 
```
```
#define VECTOR_INIT_CAPACITY 4
```
```
 
```

#define VECTOR_INIT(vec) vector vec; vector_init(&vec)

#define VECTOR_ADD(vec, item) vector_add(&vec, (void *) item)

#define VECTOR_SET(vec, id, item) vector_set(&vec, id, (void *) item)

#define VECTOR_GET(vec, type, id) (type) vector_get(&vec, id)

#define VECTOR_DELETE(vec, id) vector_delete(&vec, id)

#define VECTOR_TOTAL(vec) vector_total(&vec)

#define VECTOR_FREE(vec) vector_free(&vec)

```
 
```
```
typedef struct vector {
```
```
    void **items;
```
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    int capacity;
```
```
    int total;
```
```
} vector;
```
```
 
```
```
void vector_init(vector *);
```
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int vector_total(vector *);
```

static void vector_resize(vector *, int);

```
void vector_add(vector *, void *);
```
```
void vector_set(vector *, int, void *);
```
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void *vector_get(vector *, int);
```
```
void vector_delete(vector *, int);
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```
void vector_free(vector *);
```
```
 
```
```
#endif
```
```
 
```
```
void vector_init(vector *v) {
```
```
    v->capacity = VECTOR_INIT_CAPACITY;
```
```
    v->total = 0;
```

    v->items = malloc(sizeof(void *) * v->capacity);

```
}
```
```
 
```
```
int vector_total(vector *v) {
```
```
    return v->total;
```
```
}
```
```
 
```

static void vector_resize(vector *v, int capacity) {

```
#ifdef DEBUG_ON
```

    printf("vector_resize: %d to %d\n", v->capacity, capacity);

```
#endif
```
```
 
```

    void **items = realloc(v->items, sizeof(void *) * capacity);

```
    if (items) {
```
```
        v->items = items;
```
```
        v->capacity = capacity;
```
```
    }
```
```
}
```
```
 
```

void vector_add(vector *v, void *item) {

```
    if (v->capacity == v->total)
```

        vector_resize(v, v->capacity * 2);

```
    v->items[v->total++] = item;
```
```
}
```
```
 
```

void vector_set(vector *v, int index, void *item) {

```
    if (index >= 0 && index < v->total)
```
```
        v->items[index] = item;
```
```
}
```
```
 
```

void *vector_get(vector *v, int index) {

```
    if (index >= 0 && index < v->total)
```
```
        return v->items[index];
```
```
    return NULL;
```
```
}
```
```
 
```

void vector_delete(vector *v, int index) {

```
    if (index < 0 || index >= v->total)
```
```
        return;
```
```
 
```
```
    v->items[index] = NULL;
```
```
    int i;
```

    for (i = 0; i < v->total - 1; i++) {

```
        v->items[i] = v->items[i + 1];
```
```
        v->items[i + 1] = NULL;
```
```
    }
```
```
 
```
```
    v->total--;
```
```
 
```

    if (v->total > 0 && v->total == v->capacity / 4)

        vector_resize(v, v->capacity / 2);

```
}
```
```
 
```
```
void vector_free(vector *v) {
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```
    free(v->items);
```
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}
```
```
 
```
```
int main(void) {
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```
    int i;
```
```
 
```
```
    vector v;
```
```
    vector_init(&v);
```
```
 
```
```
    vector_add(&v, "Bonjour");
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    vector_add(&v, "tout");
```
```
    vector_add(&v, "le");
```
```
    vector_add(&v, "monde");
```
```
 
```

    for (i = 0; i < vector_total(&v); i++)

        printf("%s ", (char *) vector_get(&v, i));

```
    printf("\n");
```
```
 
```
```
    vector_delete(&v, 3);
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```
    vector_delete(&v, 2);
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    vector_delete(&v, 1);
```
```
 
```
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    vector_set(&v, 0, "Hello");
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```
    vector_add(&v, "World");
```
```
 
```

    for (i = 0; i < vector_total(&v); i++)

        printf("%s ", (char *) vector_get(&v, i));

```
    printf("\n");
```
```
 
```
```
    vector_free(&v);
```
```
}
```

Output:

$ gcc VariableLengthArray.c
$ ./a.out
 
Bonjour tout le monde 
Hello World

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