DSA0 - Pointers

https://bit.ly/dsa_pointers



#include <stdio.h>

int main() {
    int x = 10;
    int *p = &x;   // & : address-of. p now holds x's address
    *p = 20;       // * : dereference. "go to that address, treat as int"
               // x is now 20
    printf("%d",x);
}



#include <stdio.h>

int main() {
    int x = 10;
    int *p = &x;   // & : address-of. p now holds x's address
    *p = 20;       // * : dereference. "go to that address, treat as int"
               // x is now 20
    printf("%d",p);
}



#include <stdio.h>

int main() {
    int x = 10;
    int *p = &x;   // & : address-of. p now holds x's address
    *p = 20;       // * : dereference. "go to that address, treat as int"
               // x is now 20
    printf("%p",p);
}



#include <stdio.h>
int main() {
    int a = 3;
    int *pa = &a;

    printf("%p %p \n", &a, pa);
    printf("%d %d", a, *pa);
    return 0;
}






#include <stdio.h>
int sum(int a, int b)
{
    return a+b;
}

int main() {
    int a,b;
    scanf("%d %d", &a,&b);
    int c = sum(a, b);
    printf("%d", c);
}




#include <stdio.h>
void increment(int a)
{
    a = a+1;
    return;
}

int main() {
    int a,b;
    scanf("%d", &a);
    increment(a);
    printf("%d", a);
}




#include <stdio.h>
void increment(int *a)
{
    a = a+1;
    return;
}

int main() {
    int a,b;
    scanf("%d", &a);
    increment(&a);
    printf("%d", a);
}



#include <stdio.h>
void increment(int *a)
{
    *a = *a+1;
    return;
}

int main() {
    int a,b;
    scanf("%d", &a);
    increment(&a);
    printf("%d", a);
}





#include <stdio.h>
int sum(int *a, int *b)
{
    return *a + *b;
}

int main() {
    int a,b;
    scanf("%d %d", &a,&b);
    int c = sum(&a, &b);
    printf("%d", c);
}




#include <stdio.h>
int sum(int A[], int n)
{
    int total = 0;
    for(int i=0 ; i < n; i++)
    {
        total += A[i];
    }
    A[1] = 100;
    return total;
}

int main() {
    int num[5] = {1,2,3,4,5};
    int c = sum(num, 5);
    printf("%d",num[1]);
    return 0;
}




#include <stdio.h>

int main() {
    int num[5] = {1, 2, 3, 4, 5};
    int *p = num;

    for (int i = 0; i < 5; i++)
    {
        printf("%d", p[i]);
    }
    return 0;
}



#include <stdio.h>

int main() {
    int num[5] = {1, 2, 3, 4, 5};
    int *p = num;

    for (int i = 0; i < 5; i++)
    {
        printf("%d", *(p+i));
    }
    return 0;
}




#include <stdio.h>

int main() {
    int num[5] = {1, 2, 3, 4, 5};
    int *p = num;

    for (int i = 0; i < 5; i++)
    {
        printf("%d", *p);
        p++;
    }
    return 0;
}





#include <stdio.h>

void reverse(int *A, int n)
{
    int *left = A;
    int *right = A + n - 1;
    while (left < right)
    {
        int temp = *left;
        *left = *right;
        *right = temp;
        left++;
        right--;
    }
}

int main() {
    int num[6] = {1, 2, 3, 4, 5, 6};
    reverse(num, 6);
    return 0;
}





#include <stdio.h>
int sum(int *A, int n)
{
    int total = 0;
    for(int i=0 ; i < n; i++)
    {
        total += A[i];
    }
    A[1] = 100;
    return total;
}

int main() {
    int num[5] = {1,2,3,4,5};
    int c = sum(num, 5);
    printf("%d",num[1]);
    return 0;
}




#include <stdio.h>
int sum(int *A, int n)
{
    int total = 0;
    for(int i=0 ; i < n; i++)
    {
        total += *(A+i);
    }
    A[1] = 100;
    return total;
}

int main() {
    int num[5] = {1,2,3,4,5};
    int c = sum(num, 5);
    printf("%d",num[1]);
    return 0;
}




#include <stdio.h>
int sum(int A[], int n)
{
    int total = 0;
    for(int i=0 ; i < n; i++)
    {
        total += *(A+i);
    }
    A[1] = 100;
    return total;
}

int main() {
    int num[5] = {1,2,3,4,5};
    int c = sum(num, 5);
    printf("%d",num[1]);
    return 0;
}






#include <stdio.h>
int *create()
{
    int num[5] = {1,2,3,4,5};
    return num;
}

int main() {
    int *p = create();
    return 0;
}




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

int *create()
{
    int *num = malloc(5 * sizeof(int));
    if (num == NULL)
    {
        printf("Could not allocate");
        return NULL;
    }

    for(int i = 0;i<5; i++)
      num[i] = (i+1);
    return num;
}

int main() {
    int *p = create();
    free(p);
    return 0;
}





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

int main() {
    int arr[5];
    int *num = malloc(5 * sizeof(int));
    free(num);
    return 0;
}





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

int *add(int A[], int n, int num)
{
    int *arr = malloc((n + 1) * sizeof(int));
    if (arr == NULL)
    {
        printf("Could not allocate");
        return NULL;
    }
    for (int i = 0; i < n; i++)
    {
        arr[i] = A[i];
    }
    arr[n] = num;
    return arr;
}

int main() {
    int A[5] = {10, 20, 30, 40, 50};
    int *p = add(A, 5, 60);
    int *q = add(p, 6, 70);
    free(p);
    free(q);
    return 0;
}




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

int *add(int A[], int n, int num)
{
    int *arr = malloc((n + 1) * sizeof(int));
    if (arr == NULL)
    {
        printf("Could not allocate");
        return NULL;
    }
    for (int i = 0; i < n; i++)
    {
        arr[i] = A[i];
    }
    arr[n] = num;
    return arr;
}

int main() {
    int *arr = NULL;
    int n = 0, num;
    while (1)
    {
        scanf("%d", &num);
        if (num == -1)
            break;
        int *newarr = add(arr, n, num);
        if (newarr == NULL)
        {
            printf("Program failed");
            break;
        }
        free(arr);
        arr = newarr;
        n++;
    }
    free(arr);
    return 0;
}




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

int *remove_at(int *arr, int n, int index)
{
    int *newarr = malloc((n - 1) * sizeof(int));
    if (newarr == NULL)
    {
        printf("Could not allocate");
        return NULL;
    }
    int *p = newarr;
    for (int i = 0; i < n; i++)
    {
        if (i == index)
        {
            arr++;
            continue;
        }
        *p = *arr;
        arr++;
        p++;
    }
    return newarr;
}

int main() {
    int A[5] = {1, 2, 3, 4, 5};
    int *p = remove_at(A, 5, 2);
    free(p);
    return 0;
}