I need help with my code. I have to find out every possible key in Ceaser cipher. I have upper a lower letters in my message and nothing else. But my keys are repeating in my code, but I need every key unique. Pls help.
#include <stdio.h>
#include <string.h>
#include <ctype.h>
char cryptedText[]; //here could be any crypted text
int main()
{
for (int key = 0; key <= 52; ++key)
{
for (int i = 0; i < strlen(cryptedText); ++i)
{
if (cryptedText[i] >= 'A' && cryptedText[i] <= 'Z')
{
printf("%c", ((cryptedText[i] - 'A' + key)%26 + 'A'));
}
else
{
printf("%c", ((cryptedText[i] - 'a' + key)%26 + 'a'));
}
}
printf("Number of key %d\n", key);
}
return 0;
}
You need some way of keeping track of what keys you have already extracted. Maybe store them in a set, which is designed to only store unique values. Then you can print out all the values from the set at the end.
Related
I am shifting from Python to C so bit rusty on the semantics as well as coding habit. In Python everything is treated as an object and objects are passed to functions. This is not the case in C so I want to increment an integer using pointers. What is the correct assignment to do so. I want to do it the following way but have the assignments wrong:
#include <stdio.h>
int i = 24;
int increment(*i){
*i++;
return i;
}
int main() {
increment(&i);
printf("i = %d, i);
return 0;
}
I fixed your program:
#include <stdio.h>
int i = 24;
// changed from i to j in order to avoid confusion.
// note you could declare the return type as void instead
int increment(int *j){
(*j)++;
return *j;
}
int main() {
increment(&i);
printf("i = %d", i);
return 0;
}
Your main error was the missing int in the function's argument (also a missing " in the printf).
Also I would prefer using parentheses in expressions as *j++ and specify exactly the precedence like I did in (*j)++, because I want to increment the content of the variable in the 'j' location not to increment the pointer - meaning to point it on the next memory cell - and then use its content.
I basically wrote a code in which I take two command line arguments one being the type of file that I want to search in my directory and they other being the amount I want(which is not implemented yet, but I can fix that)
The code is like so:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#define sizeFileName 500
#define filesMax 5000
int cmpfunc( const void *a, const void *b) {
return *(char*)a + *(char*)b;
}
int main( int argc, char ** argv) {
FILE * fp = popen( "find . -type f", "r");
char * type = argv[1];
char * extension = ".";
char* tExtension;
tExtension = malloc(strlen(type)+1+4);
strcpy(tExtension, extension);
strcat(tExtension, type);
// printf("%s\n",tExtension);
int amount = atoi(argv[2]);
//printf("%d\n",amount);
char buff[sizeFileName];
int nFiles = 0;
char * files[filesMax];
while(fgets(buff,sizeFileName,fp)) {
int leng = strlen(buff) - 1;
if (strncmp(buff + leng - 4, tExtension, 4) == 0){
files[nFiles] = strndup(buff,leng);
//printf("\t%s\n", files[nFiles]);
nFiles ++;
}
}
fclose(fp);
printf("Found %d files\n", nFiles);
long long totalBytes = 0;
struct stat st;
// sorting based on byte size from greatest to least
qsort(files, (size_t) strlen(files), (size_t) sizeof(char), cmpfunc);
for(int i = 0;i< nFiles; i ++) {
if(0!= stat(files[i],&st)){
perror("stat failed:");
exit(-1);
}
totalBytes += st.st_size;
printf("%s : %ld\n",files[i],st.st_size);
}
printf("Total size: %lld\n", totalBytes);
// clean up
for(int i = 0; i < nFiles ; i ++ ) {
free(files[i]);
}
return 0;
}
So far I have every section set up properly, upon running the code say $./find ini 5, it would print out all the ini files followed by their byte size(it's currently ignore the 5). However, for the qsort(), I'm not exactly sure how I would sort the contents of char * files as while it holds the pathnames, I had to use stat to get the byte sizes, how would I print out a sorted version of my print statements featuring the first statement being the most bytes and finishes at the least bytes?
If we suppose your input is valid, your question could be simplified with:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define filesMax 5000
int cmpfunc(const void const *a, const void *b) { return *(char *)a + *(char *)b; }
int main(void) {
int nFiles = 4;
char *files[filesMax] = {"amazing", "hello", "this is a file", "I'm a bad file"};
qsort(files, strlen(files), sizeof(char), cmpfunc);
for (int i = 0; i < nFiles;; i++) {
printf("%s\n", files[i]);
}
}
If you compile with warning that give you:
source_file.c:11:23: warning: incompatible pointer types passing 'char *[5000]' to parameter of type 'const char *' [-Wincompatible-pointer-types]
qsort(files, strlen(files), sizeof(char), cmpfunc);
^~~~~
qsort() expect the size of your array (or in your case a subsize) and it's also expect the size of one element of your array. In both you wrongly give it to it. Also, your compare function doesn't compare anything, you are currently adding the first bytes of both pointer of char, that doesn't make a lot of sense.
To fix your code you must write:
qsort(files, nFiles, sizeof *files, &cmpfunc);
and also fix your compare function:
int cmpfunc_aux(char * const *a, char * const *b) { return strcmp(*a, *b); }
int cmpfunc(void const *a, void const *b) { return cmpfunc_aux(a, b); }
also size should be of type size_t:
size_t nFiles = 0;
Don't forget that all informations about how to use a function are write in their doc.
how would I print out a sorted version of my print statements featuring the first statement being the most bytes and finishes at the least bytes?
Your code don't show any clue that your are trying to do that, you are currently storing name file and only that. How do you expect sort your file with an information you didn't acquired ?
However, that simple create a struct that contain both file name and size, acquire information needed to sort it and sort it:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <inttypes.h>
struct file {
off_t size;
char *name;
};
int cmpfunc_aux(struct file const *a, struct file const *b) {
if (a->size > b->size) {
return -1;
} else if (a->size < b->size) {
return 1;
} else {
return 0;
}
}
int cmpfunc(void const *a, void const *b) { return cmpfunc_aux(a, b); }
#define filesMax 5000
int main(void) {
size_t nFiles = 4;
struct file files[filesMax] = {{42, "amazing"},
{21, "hello"},
{168, "this is a file"},
{84, "I'm a bad file"}};
qsort(files, nFiles, sizeof *files, &cmpfunc);
for (size_t i = 0; i < nFiles; i++) {
printf("%s, %" PRId64 "\n", files[i].name, (intmax_t)files[i].size);
}
}
The function cmpfunc() provided adds the first character of each string, and that's not a proper comparison function (it should give a opposite sign value when you switch the parameters, e.g. if "a" and "b" are the strings to compare, it adds the first two characters of both strings, giving 97+98 == 195, which is positive on unsigned chars, then calling with "b" and "a" should give a negative number (and it again gives you 98 + 97 == 195), more on, it always gives the same result ---even with signed chars--- so it cannot be used as a sorting comparator)
As you are comparing strings, why not to use the standard library function strcmp(3) which is a valid comparison function? It gives a negative number if first string is less lexicographically than the second, 0 if both are equal, and positive if first is greater lexicographically than the second.
if your function has to check (and sort) by the lenght of the filenames, then you can define it as:
int cmpfunc(char *a, char *b) /* yes, you can define parameters as char * */
{
return strlen(a) - strlen(b);
}
or, first based on file length, then lexicographically:
int cmpfunc(char *a, char *b)
{
int la = strlen(a), lb = strlen(b);
if (la != lb) return la - lb;
/* la == lb, so we must check lexicographycally */
return strcmp(a, b);
}
Now, to continue helping you, I need to know why do you need to sort anything, as you say that you want to search a directory for a file, where does the sorting take place in the problem?
I am currently using codewars.com to practice my coding skills. I finished one of the problems and wanted to check what other people's solutions were and I found one I couldn't understand. It's much better than my solution and I would like to understand it more. such what does "*std" do exactly. what is the +=i doing to the min_elements and what is happening to the min elements?
long queueTime(std::vector<int> customers,int n){
std::vector<long> queues(n, 0);
for (int i : customers)
*std::min_element(queues.begin(), queues.end()) += i;
return *std::max_element(queues.cbegin(), queues.cend());
}
This was my solution:
#include <iostream>
#include <vector>
#include <array>
using namespace std;
long queueTime(std::vector<int> customers,int n){
int i = 0; //start of Queue
int count = 0; //keeps track of how many items has been
processed
int biggest = 0; //Last/largest ending item size, add to count at end
int list [n]; //Declared number of registers by size n
for(int k = 0;k<n;k++) //sets each existing register to have 0
items
{
list[k] = 0;
}
//Start of processing customers, ends when last customer is at register.
for (auto i = customers.begin(); i!=customers.end();)
{
//checks if there are free registers.
for(int index = 0; index<n && i!=customers.end();index++)
{
if(list[index]==0)
{
list[index] = *i;
i++;
}
}
//Subtract 1 from every register
int temp=0;
for (int k =0;k<n;k++)
{
if(list[k]!= 0)
{
temp = list[k];
temp = temp-1;
list[k] = temp;
}
}
//increase count of items processed
count++;
}
//calculates the largest number of items a customer has amungst the last few
customers.
for(int j=0;j<n;j++)
{
if(list[j]>biggest)
{
biggest = list[j];
}
}
//end first part
cout<<"\nCount: "<<count<<" Biggest: "<<biggest<<endl;
cout<<"End Function:"
<<"\n************************\n***************************
*******************\n"<<endl;
//answer if number of items processed + last biggest number of items.
return count+biggest;
}
The code is mapping a set of integers to n buckets and minimizing the sum of the elements assigned to a given bucket.
For each customer int i , the smallest element of the queue is incremented by i. Then the largest resulting queue value is returned.
std::vector is a qualified name lookup of an identifier within the std namespace.
min_element returns an iterator. The dereference operator (*) produces an lvalue that is incremented by a compound assignment operator (+=).
In the below code scanf() is working for getting the name from the user but fgets() is not working pls someone help me to understand why it's not working
#include <stdio.h>
#include <stdlib.h>
typedef struct university{
int roll_no;
char name[16];
}uni;
int main()
{
uni *ptr[5],soome;char i,j=0;
for(i=0;i<5;i++)
{
ptr[i]=(uni*)calloc(1,20);
if(ptr[i]==NULL)
{
printf("memory allocation failure");
}
printf("enter the roll no and name \n");
printf("ur going to enter at the address%u \n",ptr[i]);
scanf("%d",&ptr[i]->roll_no);
//scanf("%s",&ptr[i]->name);
fgets(&ptr[i]->name,16,stdin);
}
while(*(ptr+j))
{
printf("%d %s\n",ptr[j]->roll_no,ptr[j]->name);
j++;
}
return 0;
}
First of all, fgets(char *s, int n, FILE *stream) takes three argument: a pointer s to the beginning of a character array, a count n, and an input stream.
In the original application you used the address operator & to get the pointer not to the first element of the name[16] array, but to something else (to use the address operator, you should have referenced the first char in the array: name[0]).
You use a lot of magic numbers in your application (e.g. 20 as the size of the uni struct). In my sample I'm using sizeof as much as possible.
Given that you use calloc, I've used the fact that the first parameter is the number of elements of size equal to the second parameter to preallocate all the five uni struct at once.
Final result is:
#include <stdio.h>
#include <stdlib.h>
#define NUM_ITEMS (5)
#define NAME_LENGTH (16)
typedef struct university{
int roll_no;
char name[NAME_LENGTH];
} uni;
int main()
{
uni *ptr;
int i;
ptr = (uni*)calloc(NUM_ITEMS, sizeof(uni));
if(NULL == ptr) {
printf("memory allocation failure");
return -1;
}
for(i=0; i<NUM_ITEMS; i++) {
printf("enter the roll no and name \n");
printf("You're going to enter at the address: 0x%X \n",(unsigned int)&ptr[i]);
scanf("%d",&ptr[i].roll_no);
fgets(ptr[i].name, NAME_LENGTH, stdin);
}
for(i=0; i<NUM_ITEMS; i++) {
printf("%d - %s",ptr[i].roll_no,ptr[i].name);
}
free(ptr);
return 0;
}
Note: I've added a call to free(ptr); to free the memory allocated by calloc at the end of the application and a different return code if it's not possible to allocate the memory.
Operating system: IBM AIX 5.3
Compiler: xlc
Hello Everyone
I have a project that using C to process some files using multi-processes. The number of sub-processes are mainly depends on the the number of incoming files and the number of current running processes. I need a reliable method to count on how many sub-processes are running at background.
By comparing the efficiency, directly reading /proc directory may have better performance than invoking popen() to execute $ ps -ef | grep blah.
I wrote a function to read psinfo in /proc/pid/psinfo and compare the arugments.
Pseudo code is as follow:
int count = 0;
dp = opendir("/proc");
while (readdir_r(...))
{
if (dir is not a process)
return -1;
if (dir's owner is not current user)
return -2;
if (failed to open "/proc/[pid]/psinfo")
return -3;
if (failed to read "/proc/[pid]/psinfo")
return -4;
if (process's name matches the given pname)
count += 1;
}
return count;
The function generally runs perfectly at single call. However, it returns -2 or -3 or even wrong counts when embedded in while loop.
The function failed to read the attribute of /proc/pid randomly. It tells No such file or directory.
There is also a small chance to get wrong counts at the end. There seems to be an extra process with certain pid but disappeared when printing the current processes using ps.
I think there is any change were made when reading from sub-directory rapidly after parent directory were being listed.
Is there any thing I made wrong or is there any method to avoid the race condition?
Come extra information about psinfo in AIX
http://www-01.ibm.com/support/knowledgecenter/ssw_aix_53/com.ibm.aix.files/doc/aixfiles/proc.htm%23files-proc?lang=en[233]
Here is the full source code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dirent.h>
#include <sys/procfs.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
int countProcess(char *pname)
{
DIR *dir;
int fd;
int pid;
int uid;
int pcounter = 0;
struct psinfo pinfo;
struct dirent entry;
struct dirent *result;
struct stat fsstat;
char path[256];
char process_path[256];
/* Open the /proc directory */
if ((dir = opendir("/proc")) == NULL)
{
return -1;
}
/* Retrieve the current user id */
uid = getuid();
/* Walk through the /proc dir */
for (readdir_r(dir, &entry, &result); result != NULL; readdir_r(dir, &entry, &result))
{
/* See if this is a process, e.g., the dirname is a number
If not, then start off again
*/
if ((pid = atoi(entry.d_name)) == 0)
{
continue;
}
/* Get the attributes of process dir */
snprintf(process_path, sizeof(process_path), "/proc/%s", entry.d_name);
if (stat(process_path, &fsstat) == -1)
{
closedir(dir);
return -2;
}
/* Verify if the process runs by current user
If not, then start off again
*/
if (fsstat.st_uid != uid)
{
continue;
}
/* Open and read from psinfo file */
snprintf(path, sizeof(path), "/proc/%s/psinfo", entry.d_name);
if ((fd = open(path, O_RDONLY)) < 0)
{
close(fd);
closedir(dir);
return -3;
}
if (read(fd, &pinfo, sizeof(pinfo)) < 0)
{
close(fd);
closedir(dir);
return -4;
}
/* String comparison, if same, increase the counter */
if (!strcmp(pinfo.pr_psargs, pname))
{
pcounter++;
}
close(fd);
}
/* returns counter */
closedir(dir);
return pcounter;
}
Update 13/Jan/2015
Thanks to CoreyStup. The race condition can be bypassed by getprocs() function provided in procinfo.h
Here is the code for the solution
#include <stdio.h>
#include <unistd.h>
#include <procinfo.h>
#include <sys/types.h>
int countProcess(const char *pname)
{
struct procsinfo pinfo;
pid_t pid = 0;
uid_t uid;
char args[256];
int index;
int pcounter = 0;
memset(args, 0, sizeof(args));
uid = getuid();
/* Get procsinfo from internal API */
while (0 < getprocs(&pinfo, (int)sizeof(struct procsinfo), NULL, 0, &pid, 1))
{
/* Skip the process that doesn't belong to current user */
if (pinfo.pi_uid != uid)
{
continue;
}
/* Get process arguments */
if (getargs(&pinfo, sizeof(struct procsinfo), args, sizeof(args)) != 0)
{
return -1;
}
/* getargs returns the args list seperated by 0, we need to use space to replace 0 */
for (index = 0; index < 256 - 1 && !(args[index] == 0 && args[index + 1] == 0); index++)
{
if (args[index] == 0)
{
args[index] = ' ';
}
}
if (!strncmp(args, pname, strlen(pname)))
{
pcounter++;
}
}
return pcounter;
}
Try using getprocs(). I find it works better than shelling out with /proc or ps.
I gave an example here: Need help in getting the process name based on the pid in aix