C Program to show Memory Allocation

C Program to show Memory Allocation

#include<fcntl.h>
#include<stdio.h>
#include<string.h>
#include<sys/types.h>
#include<unistd.h>
#include<stdlib.h>
int main()
{
        int fd,fp,ch,l=0,q=0;
        char *name, *in, *out;
        printf("Enter the name of the file:");
        scanf("%s",name);
        fd=open(name, O_CREAT, S_IRWXU);
        if(fd!=-1)
        {
                printf("%s File is created.\n",name);
                close(fd);
                while(q==0)
                {
                        printf("Menu\n1.Rdonly\n2.Wronly\n3.Rdwr\n4.Exit\nEnter your choice:");
                        scanf("%d",&ch);
                        switch(ch)
                        {
                                case 1: fp=open(name,O_RDONLY);
                                        printf("%s File is opened with Read Only mode.\n",name);
                                        l=lseek(fp,0,SEEK_END);
                                        out=(char *) malloc(20);
                                        if(l>0)
                                        {
                                                int fd=open(name,O_RDONLY);
                                                read(fd,out,l);
                                                printf("File Data: %s\n",out);
                                                close(fd);
                                        }
                                        else
                                                printf("File is Empty...\n");
                                        close(fd);
                                        break;
                                case 2: fd=open(name,O_WRONLY);
                                        printf("%s File is opened with Write Only mode.\n",name);
 printf("Enter the Data: \n");
                                        in=(char *) malloc(20);
                                        scanf("%s",in);
                                        write(fd,in,strlen(in));
                                        printf("%s is written to the file %s\n",in,name);
                                        close(fd);
                                        break;
                                case 3: fd=open(name,O_RDWR);
                                        printf("%s File is opened with Read Write mode.\n",name);
                                        printf("Enter the Data: \n");
                                        scanf("%s",in);
                                        write(fd,in,strlen(in));
                                        l=lseek(fd,0,SEEK_END);
                                        out=(char *) malloc(20);
                                        if(l>0)
                                        {
                                                int fd=open(name,O_RDONLY);
                                                read(fd,out,l);
                                                printf("File Data: %s\n",out);
                                                close(fd);
                                        }
                                        else
                                                printf("File is Empty...\n");
                                        close(fd);
                                        break;
                                case 4: q=1;
                                        break;
                                default : printf("Your option is invalid... Try again...\n");
                        }
                }
        }
        else
                printf("Error!! %s already exists...\n",name);
        return(0);
}