Question

C++ Code error help. I am getting the error: "expression must have a constant value, the value of parameter 'n' ( declared at line 7) cannot be used as a constant" I am also getting this error at lines 65 and 66 with m and n. I do not know how to fix this. Here is my code and ive marked where the errors were with lines:

#include<iostream>
using namespace std;

// Function to allocate memory to blocks as per worst fit
// algorithm
void worstFit(int blockSize[], int m, int processSize[],
   int n)
{
   // Stores block id of the block allocated to a
   // process
------ int allocation[n]; -------- here

   // Initially no block is assigned to any process
   memset(allocation, -1, sizeof(allocation));

   // pick each process and find suitable blocks
   // according to its size ad assign to it
   for (int i = 0; i<n; i++)
   {
       // Find the best fit block for current process
       int wstIdx = -1;
       for (int j = 0; j<m; j++)
       {
           if (blockSize[j] >= processSize[i])
           {
               if (wstIdx == -1)
                   wstIdx = j;
               else if (blockSize[wstIdx] < blockSize[j])
                   wstIdx = j;
           }
       }

       // If we could find a block for current process
       if (wstIdx != -1)
       {
           // allocate block j to p[i] process
           allocation[i] = wstIdx;

           // Reduce available memory in this block.
           blockSize[wstIdx] -= processSize[i];
       }
   }

   cout << "\nProcess No.\tProcess Size\tBlock no.\n";
   for (int i = 0; i < n; i++)
   {
       cout << " " << i + 1 << "\t\t" << processSize[i] << "\t\t";
       if (allocation[i] != -1)
           cout << allocation[i] + 1;
       else
           cout << "Not Allocated";
       cout << endl;
   }
}

// Driver code
int main()
{
   int m, n;
   cout << "Enter no. of memory partitions: ";
   cin >> m;
   cout << "\nEnter the number of processes:";
   cin >> n;

------ int blockSize[m];--------- here
------- int processSize[n];------- here
   cout << "\nEnter size of each mermory partition: \n";
   for (int i = 1; i <= m; i++) {
       cout << "Partition no." << i << ":";
       cin >> blockSize[i];
   }

   cout << "\nEnter the size of each process :-\n";
   for (int i = 1; i <= n; i++) {
       cout << "Process no. " << i << ":";
       cin >> processSize[i];
   }

   worstFit(blockSize, m, processSize, n);

   return 0;
}

Answer 1

I have debugged your code completely, and it is working fine now.

Errors have been resolved

I will tell you your mistakes

1. You are creating an array  int blockSize[m]; (size of the block is m, elements will be stored from 0 to m-1, right?)
2. for (int i = 1; i <= m; i++) {
          cout << "Partition no." << i << ":";
          cin >> blockSize[i];
   } Here you are using memory blockSize[m] which is not defined, and blockSize[0] is getting filled with random value. So i have initialised i from 0 until i<m.
3. for (int i = 1; i <= n; i++) {
          cout << "Process no. " << i << ":";
          cin >> processSize[i];
      } Same is the scenario with this. So i have initialised i from 0 until i<n

Here is the corrected code.

#include<iostream>
#include<bits/stdc++.h>
using namespace std;

// Function to allocate memory to blocks as per worst fit
// algorithm
void worstFit(int blockSize[], int m, int processSize[],
int n)
{
// Stores block id of the block allocated to a
// process
int allocation[n];

// Initially no block is assigned to any process
memset(allocation, -1, sizeof(allocation));

// pick each process and find suitable blocks
// according to its size ad assign to it
for (int i = 0; i<n; i++)
{
// Find the best fit block for current process
int wstIdx = -1;
for (int j = 0; j<m; j++)
{
if (blockSize[j] >= processSize[i])
{
if (wstIdx == -1)
wstIdx = j;
else if (blockSize[wstIdx] < blockSize[j])
wstIdx = j;
}
}

// If we could find a block for current process
if (wstIdx != -1)
{
// allocate block j to p[i] process
allocation[i] = wstIdx;

// Reduce available memory in this block.
blockSize[wstIdx] -= processSize[i];
}
}

cout << "\nProcess No.\tProcess Size\tBlock no.\n";
for (int i = 0; i < n; i++)
{
cout << " " << i + 1 << "\t\t" << processSize[i] << "\t\t";
if (allocation[i] != -1)
cout << allocation[i] + 1;
else
cout << "Not Allocated";
cout << endl;
}
}

// Driver code
int main()
{
int m, n;
cout << "Enter no. of memory partitions: ";
cin >> m;
cout << "\nEnter the number of processes:";
cin >> n;

int blockSize[m];
int processSize[n];
cout << "\nEnter size of each mermory partition: \n";
for (int i = 0; i <m; i++) {
cout << "Partition no." << i << ":";
cin >> blockSize[i];
}

cout << "\nEnter the size of each process :-\n";
for (int i = 0; i <n; i++) {
cout << "Process no. " << i << ":";
cin >> processSize[i];
}

worstFit(blockSize, m, processSize, n);

return 0;
}

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