Create a function to copy n char like strcpy in C - c

Question

#include <stdio.h>
#include <stdlib.h>
void nhap(char* &scr, int *n)
{
do
{
printf("Input the string length:\n");
scanf_s("%d", n);
} while (n < 0);
scr = (char*)malloc(*n * sizeof(char));
for (int i = 0; i < *n; i++)
{
scanf_s("%c", (scr + i));
}
}
void xuat(char* scr, int n)
{
printf("\nThe content of string: ");
for (int i = 0; i < n; i++)
{
printf("%c", *(scr + i));
}
}
char* StringNCopy(char* dest, char* scr, int n)
{
if (n == NULL)
{
return NULL;
}
dest = (char*)realloc(dest, n * sizeof(char));
for (int i = 0; i < n; i++)
{
for (int j = *(scr + n); j > 0; j--)
{
*(dest + i) = *(scr + j);
}
}
*(dest + n) = '\0';
return dest;
}
void main()
{
char *a;
char *b=NULL;
int n;
nhap(a, &n);
xuat(a, n);
StringNCopy(b, a, 4);
printf("%s", *b);
free(a);
}
Excuse me, I have a problem, I want to create a function likes strcpy but there is some errors I can't fix by myself. I think it will copy n elements from char* scr to char* dest, but when I run my code, it crashed. Can you help me to fix the code and explain to me. I'm very thankful.

Answer 1

The for loops should be in this way
for (int i = 0; i < n; i++)
{
*(dest + i) = *(scr + i);
}
You dont need nested for loops for this, because you just need to traverse the array once and copy the values.
Corrected program
#include <stdio.h>
#include <stdlib.h>
void nhap(char* &scr, int *n)
{
do
{
printf("Input the string length:\n");
scanf("%d", n);
} while (n < 0);
scr = (char*)malloc((*n+1) * sizeof(char)); //allocated size should be n+1
fflush(stdin);
for (int i = 0; i < *n; i++)
{
scanf("%c", (scr+i ));
}
}
void xuat(char* scr, int n)
{
printf("\nThe content of string: ");
for (int i = 0; i < n; i++)
{
printf("%c", *(scr + i));
}
}
void StringNCopy(char* &dest, char* &scr, int n) //no need to return the string aas you can pass it as reference
{
if (n == NULL)
{
return;
}
dest = (char*)realloc(dest, (n+1) * sizeof(char)); //alloted size should be n+1
for (int i = 0; i < n; i++)
{
*(dest + i) = *(scr + i); //no need of nested loops
}
*(dest + n) = '\0';
}
int main()
{
char *a;
char *b=NULL;
int n;
nhap(a, &n);
xuat(a, n);
StringNCopy(b, a, 4);
printf("\n6%s", b);
free(a);
}
Tested and working fine.Observe the errors mentioned in comments