First Fit Algorithm in C and C++

Here you will learn about first fit algorithm in C and C++ with program examples.

There are various memory management schemes in operating system like first fit, best fit and worst fit. In this section we will talk about first fit scheme.

What is First Fit Memory Management Scheme?

In this scheme we check the blocks in a sequential manner which means we pick the first process then compare it’s size with first block size if it is less than size of block it is allocated otherwise we move to second block and so on.

When first process is allocated we move on to the next process until all processes are allocated.

Also Read: Best Fit Algorithm in C and C++

First Fit Algorithm

1. Get no. of Processes and no. of blocks.
2. After that get the size of each block and process requests.
3. Now allocate processes
   if(block size >= process size)
   //allocate the process
   else
   //move on to next block
4. Display the processes with the blocks that are allocated to a respective process.
5. Stop.

Program for First Fit Algorithm in C

#include<stdio.h>

void main()
{
	int bsize[10], psize[10], bno, pno, flags[10], allocation[10], i, j;

	for(i = 0; i < 10; i++)
	{
		flags[i] = 0;
		allocation[i] = -1;
	}
	
	printf("Enter no. of blocks: ");
	scanf("%d", &bno);
	
	printf("\nEnter size of each block: ");
	for(i = 0; i < bno; i++)
		scanf("%d", &bsize[i]);

	printf("\nEnter no. of processes: ");
	scanf("%d", &pno);
	
	printf("\nEnter size of each process: ");
	for(i = 0; i < pno; i++)
		scanf("%d", &psize[i]);
	for(i = 0; i < pno; i++)         //allocation as per first fit
		for(j = 0; j < bno; j++)
			if(flags[j] == 0 && bsize[j] >= psize[i])
			{
				allocation[j] = i;
				flags[j] = 1;
				break;
			}
	
	//display allocation details
	printf("\nBlock no.\tsize\t\tprocess no.\t\tsize");
	for(i = 0; i < bno; i++)
	{
		printf("\n%d\t\t%d\t\t", i+1, bsize[i]);
		if(flags[i] == 1)
			printf("%d\t\t\t%d",allocation[i]+1,psize[allocation[i]]);
		else
			printf("Not allocated");
	}
}

Program for First Fit Algorithm in C++

#include<iostream>

using namespace std;

int main()
{
	int bsize[10], psize[10], bno, pno, flags[10], allocation[10], i, j;

	for(i = 0; i < 10; i++)
	{
		flags[i] = 0;
		allocation[i] = -1;
	}
	
	cout<<"Enter no. of blocks: ";
	cin>>bno;
	
	cout<<"\nEnter size of each block: ";
	for(i = 0; i < bno; i++)
		cin>>bsize[i];

	cout<<"\nEnter no. of processes: ";
	cin>>pno;
	
	cout<<"\nEnter size of each process: ";
	for(i = 0; i < pno; i++)
		cin>>psize[i];
	for(i = 0; i < pno; i++)         //allocation as per first fit
		for(j = 0; j < bno; j++)
			if(flags[j] == 0 && bsize[j] >= psize[i])
			{
				allocation[j] = i;
				flags[j] = 1;
				break;
			}
	
	//display allocation details
	cout<<"\nBlock no.\tsize\t\tprocess no.\t\tsize";
	for(i = 0; i < bno; i++)
	{
		cout<<"\n"<< i+1<<"\t\t"<<bsize[i]<<"\t\t";
		if(flags[i] == 1)
			cout<<allocation[i]+1<<"\t\t\t"<<psize[allocation[i]];
		else
			cout<<"Not allocated";
	}
	
	return 0;
}

Output

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