Runtime error: insertatIndex - c

Question

#include <stdio.h>
#include <malloc.h>
int insertAt(int *Arr, int len, int num) {
for (int i = 0; i < len; ++i) {
if (num <= Arr[0])
return 0;
else if (num >= Arr[len])
return len + 1;
else if (num >= Arr[i - 1] && num <= Arr[i])
return i;
}
}
int * sortedArrayInsertNumber(int *Arr, int len, int num){
int *output = (int *)malloc((len + 1)*sizeof(int));
if (len <= 0)
return NULL;
for (int i = 0, j = 0; j <= len+1; ++i, ++j) {
if (i == insertAt(Arr, len, num) && j==i) {
output[j] = num;
--i;
}
else if(insertAt(Arr,len,num)==len+1) {
output[j] = num;
}
else {
output[j] = Arr[i];
}
}
return output;
}
int main() {
int input[5] = {2,4,6,8,10};
int *out = (int*)malloc(6*sizeof(int));
out = sortedArrayInsertNumber(input, 5, 12);
for(int i=0;i<6;++i) {
printf("%d\n", out[i]);
}
}
When I try out this test case, it gives me a runtime error sometimes. Other times, it outputs:
2
4
6
8
10
12
Which makes no sense?
Also, is there a way to make my code better?
The question requires me to insert a value num at its appropriate index.

Answer 1

In the function insertAt there is at least two attempts to access memory beyond the array. The first one is in the statement
else if (num >= Arr[len])
^^^^
And the second one is in the statement
else if (num >= Arr[i - 1] && num <= Arr[i])
^^^^^^
when the variable i is equal to 0.
The function sortedArrayInsertNumber starts with a potential memory leak when the variable len is equal at least 0 because at first a memory is allocated and then there is exit from the function with A NULL pointer.
int * sortedArrayInsertNumber(int *Arr, int len, int num){
int *output = (int *)malloc((len + 1)*sizeof(int));
if (len <= 0)
return NULL;
// ...
Also it is a bad idea when the length of an array has type int instead of type size_t.
To call several times the function insertAt in the function sortedArrayInsertNumber does not make sense and breaks the loop.
In the main there is again a memory leak
int *out = (int*)malloc(6*sizeof(int));
out = sortedArrayInsertNumber(input, 5, 12);
The program can look the following way.
#include <stdio.h>
#include<stdlib.h>
size_t insertAt( const int *a, size_t n, int num )
{
size_t i = 0;
while ( i < n && !( num < a[i] ) ) i++;
return i;
}
int * sortedArrayInsertNumber( const int *a, size_t n, int num )
{
int *b = malloc( ( n + 1 ) * sizeof( int ) );
if ( b )
{
size_t pos = insertAt( a, n, num );
size_t i = 0;
for ( ; i < pos; i++ ) b[i] = a[i];
b[i] = num;
for ( ; i < n; i++ ) b[i+1] = a[i];
}
return b;
}
int main(void)
{
int input[] = { 2, 4, 6, 8, 10 };
const size_t N = sizeof( input ) / sizeof( *input );
int *out = sortedArrayInsertNumber( input, N, 12 );
if ( out )
{
for ( size_t i = 0; i < N + 1; i++ )
{
printf( "%d ", out[i] );
}
putchar( '\n' );
}
free( out );
return 0;
}
Its output is
2 4 6 8 10 12
Instead of the loops in the function sortedArrayInsertNumber you can use standard C function memcpy declared in header <string.h>.