How to set last Unused drive letter to Combobox in MFC (VC++) ?
My code is like this :
TCHAR g_szDrvMsg[] = _T("A:\n");
int main(int argc, char* argv[]) {
ULONG uDriveMask = _getdrives();
if (uDriveMask == 0)
{
printf( "_getdrives() failed with failure code: %d\n",
GetLastError()); //So GetLastError retuns a sring or char*?
}
else
{
printf("The following logical drives are being used:\n");
while (uDriveMask) {
if (!(uDriveMask & 1))
m_objCmbdrive.AddString(g_szDrvMsg);
++g_szDrvMsg[0];
uDriveMask >>= 1;
}
}
}
m_objCmbdrive.SetCurSel();
What value i should pass to SetCurSel to set Drive letter in descending order.
This code gives me Drive All drive letters which are being used in the system.
how to get all unused one out ?
To select the last item in your combobox, you can do:
m_objCmbdrive.SetCurSel(m_objCmbdrive.GetCount() - 1);
To fill your combobox with unused drive letters in descending order, use the InsertString() method:
for (int i = 0; i < 26; ++i) {
if (!(uDriveMask & 1)) {
m_objCmbdrive.InsertString(0, g_szDrvMsg);
}
++g_szDrvMsg[0];
uDriveMask >>= 1;
}
Related
I keep getting an error around handling duplicate characters in key when checking my code for the substitution problem within pset2 of the cs50 course 2020. My code and further details are below - can anyone please help with this? Thanks
The error message it gives me is
:( handles duplicate characters in key
timed out while waiting for program to exit
When I check my code for duplicate characters it seems to work fine (printing Usage: ./substitution key and ending the program)
Code below
# include <stdio.h>
# include <cs50.h>
# include <string.h>
# include <stdlib.h>
# include <ctype.h>
int main(int argc, string argv[])
{
// Check that only one argument submitted
if (argc == 2)
{
// Check that key contains 26 characters
int keylen = strlen(argv[1]);
if (keylen == 26)
{
// Check that all characters are letters
for (int i = 0; i < keylen; i++)
{
bool lettercheck = isalpha(argv[1][i]);
if (lettercheck == true)
{
// THIS IS CAUSING ERROR - Check that no letters have been repeated - put all in lowercase to do so
for (int n = 0; n < i; n++)
{
char currentletter = argv[1][i];
char previousletter = argv[1][i - 1];
if (tolower(currentletter) == tolower(previousletter))
{
printf("Usage: ./substitution key\n");
return 1;
}
}
}
else
{
printf("Usage: ./substitution key\n");
return 1;
}
}
}
else
{
printf("Key must contain 26 characters.\n");
return 1;
}
}
else
{
printf("Usage: ./substitution key\n");
return 1;
}
// Get user input
string input = get_string("plaintext: ");
//Transform input using key
for(int i = 0; i < strlen(input); i++)
{
char currentletter = input[i];
int testlower = islower(currentletter);
int testupper = isupper(currentletter);
if (testupper > 0)
{
int j = input[i] - 65;
input[i] = toupper(argv[1][j]);
}
else if (testlower > 0)
{
int j = input[i] - 97;
input[i] = tolower(argv[1][j]);
}
}
printf("ciphertext: %s\n", input);
}
Edit:
Figured out solution - problem was with the second for loop was iterating against i - 1 times instead of n times
Code should have been
charpreviouslletter = argv[1][n]
instead of
charpreviousletter = argv[1][i - 1]
for (int n = 0; n < i; n++)
{
char currentletter = argv[1][i];
char previousletter = argv[1]**[i - 1]**
In this loop-
// THIS IS CAUSING ERROR - Check that no letters have been repeated - put all in lowercase to do so
for (int n = 0; n < i; n++)
{
char currentletter = argv[1][i];
char previousletter = argv[1][i - 1];
if (tolower(currentletter) == tolower(previousletter))
{
printf("Usage: ./substitution key\n");
return 1;
}
}
you're comparing only the current character to the previous character. This doesn't work for strings like abcdefca
Notice how, c and a have duplicates - but they're not right next to their originals and hence your logic won't find these duplicates. Your logic will only work for duplicates that are next to each other such as aabcddef.
Instead, you need to take a note of which characters you've encountered whilst looping through. If you encounter a character that you have already encountered, you know there's a duplicate.
Thankfully, the key is only expected to contain all 26 characters of the alphabet without any duplicates. This means you can simply have an int array of 26 slots - each slot counts the number of appearances of the letter at that index. 0th index stands for 'a', 1st for 'b' and so on.
This way, you can very easily get the index of an alphabetic character using letter - 'a', where letter is the alphabetic character. So if the letter was a, you'd get 0, which is indeed the index of 'a'
Also, you have a nested loop while traversing the key, this nested loop also traverses through the key. Except it does it only up until a certain index, the index being the current index of the outer loop. This seems wasteful and weird. Why not simply loop through once, check if current character is an alphabetic letter and also check if this letter has been encountered before. That's all you have to do!
int letter_presence[26];
char upperletter;
string key = argv[1];
if (strlen(key) == KEY_LEN)
{
for (int index = 0; index < KEY_LEN; index++)
{
if (!isalpha(key[index]))
{
// Wrong key - invalid character
printf("Usage: ./substitution key\n");
return 1;
}
if (letter_presence[tolower(key[index]) - 'a'] == 0)
{
// This letter has not been encountered before
letter_presence[upperletter - 'A'] = 1;
}
else
{
// Wrong key - Duplicate letters
return 1;
}
}
// All good
}
My doubts are as follows :
1 : how to send 'str' from function 'fun' , So that i can display it in main function.
2 : And is the return type correct in the code ?
2 : the current code is displaying some different output.
char * fun(int *arr)
{
char *str[5];
int i;
for(i=0;i<5;i++)
{
char c[sizeof(int)] ;
sprintf(c,"%d",arr[i]);
str[i] = malloc(sizeof(c));
strcpy(str[i],c);
}
return str;
}
int main()
{
int arr[] = {2,1,3,4,5},i;
char *str = fun(arr);
for(i=0;i<5;i++)
{
printf("%c",str[i]);
}
return 0;
}
how to send 'str' from function 'fun' , So that i can display it in main function.
This is the way:
char* str = malloc( size );
if( str == NULL ) {
fprintf( stderr,"Failed to malloc\n");
}
/* Do stuff with str, use str[index],
* remember to free it in main*/
free(str);
And is the return type correct in the code ?
No, Probably char** is the one you need to return.
the current code is displaying some different output.
Consider explaining what/why do you want to do ? The way you have written, seems completely messed up way to me. You're passing array of integer but not its length. How is the fun() supposed to know length of array? Another problem is array of pointers in fun().
You can't write a int to a char (See the both size). So I used char array instead.
However, I'm not sure if this is what you want to do (might be a quick and dirty way of doing it):
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char**
fun(int *arr, int size)
{
char **str = malloc( sizeof(char*)*size );
if( str == NULL ) {
fprintf( stderr, "Failed malloc\n");
}
int i;
for(i=0;i<5;i++) {
str[i] = malloc(sizeof(int));
if( str == NULL ) {
fprintf( stderr, "Failed malloc\n");
}
sprintf(str[i],"%d",arr[i]);
}
return str;
}
int
main()
{
int arr[] = {2,1,3,4,5},i;
char **str = fun(arr, 5);
for(i=0;i<5;i++) {
printf("%s\n",str[i]);
free(str[i]);
}
free(str);
return 0;
}
I made these changes to your code to get it working:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char **fun(int *arr)
{
char **str = malloc(sizeof(char *) * 5);
int i;
for(i = 0; i < 5; i++) {
if ((arr[i] >= 0) && (arr[i] <= 9)) {
char c[2] ;
sprintf(c, "%d", arr[i]);
str[i] = (char *) malloc(strlen(c) + 1);
strcpy(str[i],c);
}
}
return str;
}
int main()
{
int arr[] = {2, 1, 3, 4, 5}, i;
char **str = fun(arr);
for(i = 0; i < 5; i++) {
printf("%s", str[i]);
free(str[i]);
}
printf("\n");
free(str);
return 0;
}
Output
21345
I added a check to make sure that arr[i] is a single digit number. Also, returning a pointer to a stack variable will result in undefined behavior, so I changed the code to allocate an array of strings. I don't check the return value of the malloc calls, which means this program could crash due to a NULL pointer reference.
This solution differs from the others in that it attempts to answer your question based on the intended use.
how to send 'str' from function 'fun' , So that i can display it in main function.
First, you need to define a function that returns a pointer to array.
char (*fun(int arr[]))[]
Allocating variable length strings doesn't buy you anything. The longest string you'll need for 64bit unsigned int is 20 digits. All you need is to allocate an array of 5 elements of 2 characters long each. You may adjust the length to suit your need. This sample assumes 1 digit and 1 null character. Note the allocation is done only once. You may choose to use the length of 21 (20 digits and 1 null).
For readability on which values here are related to the number of digits including the terminator, I'll define a macro that you can modify to suit your needs.
#define NUM_OF_DIGITS 3
You can then use this macro in the whole code.
char (*str)[NUM_OF_DIGITS] = malloc(5 * NUM_OF_DIGITS);
Finally the receiving variable in main() can be declared and assigned the returned array.
char (*str)[NUM_OF_DIGITS] = fun(arr);
Your complete code should look like this:
Code
char (*fun(int arr[]))[]
{
char (*str)[NUM_OF_DIGITS] = malloc(5 * NUM_OF_DIGITS);
int i;
for(i=0;i<5;i++)
{
snprintf(str[i],NUM_OF_DIGITS,"%d",arr[i]); //control and limit to single digit + null
}
return str;
}
int main()
{
int arr[] = {24,1,33,4,5},i;
char (*str)[NUM_OF_DIGITS] = fun(arr);
for(i=0;i<5;i++)
{
printf("%s",str[i]);
}
free(str);
return 0;
}
Output
2413345
With this method you only need to free the allocated memory once.
I am working on the Vigenere exercise from Harvard's CS50 (in case you noticed I'm using string and not str).
My program gives me a Floating Point Exception error when I use "a" in the keyword.
It actually gives me that error
when I use "a" by itself, and
when I use "a" within a bigger word it just gives me wrong output.
For any other kind of keyword, the program works perfectly fine.
I've run a million tests. Why is it doing this? I can't see where I'm dividing or % by 0. The length of the keyword is always at least 1. It is probably going to be some super simple mistake, but I've been at this for about 10 hours and I can barely remember my name.
#include <stdio.h>
#include <cs50.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
int main (int argc, string argv[])
{
//Error message if argc is not 2 and argv[1] is not alphabetical
if (argc != 2)
{
printf("Insert './vigenere' followed by an all alphabetical key\n");
return 1;
}
else if (argv[1])
{
for (int i = 0, n = strlen(argv[1]); i < n; i++)
{
if (isalpha((argv[1])[i]) == false)
{
printf("Insert './vigenere' followed by an all alphabetical key\n");
return 1;
}
}
//Store keyword in variable
string keyword = argv[1];
//Convert all capital chars in keyword to lowercase values, then converts them to alphabetical corresponding number
for (int i = 0, n = strlen(keyword); i < n; i++)
{
if (isupper(keyword[i])) {
keyword[i] += 32;
}
keyword[i] -= 97;
}
//Ask for users message
string message = GetString();
int counter = 0;
int keywordLength = strlen(keyword);
//Iterate through each of the message's chars
for (int i = 0, n = strlen(message); i < n; i++)
{
//Check if ith char is a letter
if (isalpha(message[i])) {
int index = counter % keywordLength;
if (isupper(message[i])) {
char letter = (((message[i] - 65) + (keyword[index])) % 26) + 65;
printf("%c", letter);
counter++;
} else if (islower(message[i])) {
char letter = (((message[i] - 97) + (keyword[index])) % 26) + 97;
printf("%c", letter);
counter++;
}
} else {
//Prints non alphabetic characters
printf("%c", message[i]);
}
}
printf("\n");
return 0;
}
}
This behavior is caused by the line keyword[i] -= 97;, there you make every 'a' in the key stream a zero. Later you use strlen() on the transformed key. So when the key starts with an 'a', keywordLength therefor is set to zero, and the modulo keywordLength operation get into a division by zero. You can fix this by calculating the keyword length before the key transformation.
I have an array of 1's and 0's which is compressed in such a way that when the number of 1's is greater than 10 it writes +n+ when n in the number of 1's and when the number of 0's is greater than 10 it writes -n- when n in the number of 0's otherwise it writes them as it is.
Now the issue is, I need to decompress the array to write it back to the file. But I can't find a way to convert the number of zeros or ones to integer. It keeps giving me an error which says initializing argument 1 of ‘int atoi(const char*) and another one on the same line which says invalid conversion from ‘char’ to ‘const char*’
I'm working in Linux.
Here's a peice of my code
else if(str[i]=='+')
{
n=atoi(str[i+1]);
for(int j=0;j<n;j++)
{
strcat(temp,"1");
i=i+n-1;
}
}
This is an algorithm do "expansion" - don't ever use it in production - for example, there is no error checking, so it is not safe. It is a quick example.
char *decode(char *q)
{
char *all=NULL;
long i=0;
int n='0';
char *p;
if(*q== '+')
n='1';
++q;
i=strtol(q, NULL, 10);
all=calloc( i + 1, 1);
for(p=all; i; i--)
*p++=n;
return all;
}
char *decompress(char *dest, char *str)
{
char *p=str;
char *q=dest;
for(; *p; p++)
{
if( isdigit((int)*p) )
{
*q++=*p;
*q=0x0;
}
else // - or +
{
char *tmp=decode(p);
strcpy(q, tmp);
q=strchr(q, '\0');
free(tmp);
p=strchr(p+1, *p); // next
}
}
return dest;
}
I am new to c++ programming I have to call a function with following arguments.
int Start (int argc, char **argv).
When I try to call the above function with the code below I get run time exceptions. Can some one help me out in resolving the above problem.
char * filename=NULL;
char **Argument1=NULL;
int Argument=0;
int j = 0;
int k = 0;
int i=0;
int Arg()
{
filename = "Globuss -dc bird.jpg\0";
for(i=0;filename[i]!=NULL;i++)
{
if ((const char *)filename[i]!=" ")
{
Argument1[j][k++] = NULL; // Here I get An unhandled
// exception of type
//'System.NullReferenceException'
// occurred
j++;
k=0;
}
else
{
(const char )Argument1[j][k] = filename [j]; // Here I also i get exception
k++;
Argument++;
}
}
Argument ++;
return 0;
}
Start (Argument,Argument1);
Two things:
char **Argument1=NULL;
This is pointer to pointer, You need to allocate it with some space in memory.
*Argument1 = new char[10];
for(i=0, i<10; ++i) Argument[i] = new char();
Don't forget to delete in the same style.
You appear to have no allocated any memory to you arrays, you just have a NULL pointer
char * filename=NULL;
char **Argument1=NULL;
int Argument=0;
int j = 0;
int k = 0;
int i=0;
int Arg()
{
filename = "Globuss -dc bird.jpg\0";
//I dont' know why you have 2D here, you are going to need to allocate
//sizes for both parts of the 2D array
**Argument1 = new char *[TotalFileNames];
for(int x = 0; x < TotalFileNames; x++)
Argument1[x] = new char[SIZE_OF_WHAT_YOU_NEED];
for(i=0;filename[i]!=NULL;i++)
{
if ((const char *)filename[i]!=" ")
{
Argument1[j][k++] = NULL; // Here I get An unhandled
// exception of type
//'System.NullReferenceException'
// occurred
j++;
k=0;
}
else
{
(const char )Argument1[j][k] = filename [j]; // Here I also i get exception
k++;
Argument++;
}
}
Argument ++;
return 0;
}
The first thing you have to do is to find the number of the strings you will have. Thats easy done with something like:
int len = strlen(filename);
int numwords = 1;
for(i = 0; i < len; i++) {
if(filename[i] == ' ') {
numwords++;
// eating up all spaces to not count following ' '
// dont checking if i exceeds len, because it will auto-stop at '\0'
while(filename[i] == ' ') i++;
}
}
In the above code i assume there will be at least one word in the filename (i.e. it wont be an empty string).
Now you can allocate memory for Argument1.
Argument1 = new char *[numwords];
After that you have two options:
use strtok (http://www.cplusplus.com/reference/clibrary/cstring/strtok/)
implement your function to split a string
That can be done like this:
int i,cur,last;
for(i = last = cur = 0; cur < len; cur++) {
while(filename[last] == ' ') { // last should never be ' '
last++;
}
if(filename[cur] == ' ') {
if(last < cur) {
Argument1[i] = new char[cur-last+1]; // +1 for string termination '\0'
strncpy(Argument1[i], &filename[last], cur-last);
last = cur;
}
}
}
The above code is not optimized, i just tried to make it as easy as possible to understand.
I also did not test it, but it should work. Assumptions i made:
string is null terminated
there is at least 1 word in the string.
Also whenever im referring to a string, i mean a char array :P
Some mistakes i noticed in your code:
in c/c++ " " is a pointer to a const char array which contains a space.
If you compare it with another " " you will compare the pointers to them. They may (and probably will) be different. Use strcmp (http://www.cplusplus.com/reference/clibrary/cstring/strcmp/) for that.
You should learn how to allocate dynamically memory. In c you can do it with malloc, in c++ with malloc and new (better use new instead of malloc).
Hope i helped!
PS if there is an error in my code tell me and ill fix it.