C/C++ Programming Questions Not Worth Their Own Thread

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icantfindaname: Jul 1, 2008

Hey, I can't for the life of me figure out what's wrong with this program. It's supposed to take a two dimensional array and find the elements that are larger than their neighbors

code:

#include <stdio.h>

#define size 3

int IsLarger (int array[size + 2][size + 2], int i, int j);

main ()
{
	srand( (unsigned)time( NULL ) );

	int array[size+2][size+2], i, j;

	for (i = 0; i < size + 2; i++) {
		for (j = 0; j < size + 2; j++) {
			array[i][j] = -32766;
		}
	}

	for (i = 1; i <= size; i++) {
		for (j = 1; j <= size; j++) {
			printf("\nPlease enter an integer: ");
			scanf("%d", &array[i][j]);
		}
	}

	for (i = 1; i <= size; i++) {
		for(j = 1; j <= size; j++) {
			if (IsLarger(array, i, j) == 1) printf ("%d in location (%d, %d)\n", array[i][j], i, j);
		}
	}

	for (i = 1; i <= size; i++) {
		for(j = 1; j <= size; j++) {
			printf ("[%d]", array[i][j]);
		}
		printf("\n");
	}
}

int IsLarger (int array[size + 2][size + 2], int i, int j)
{
	int k, l;
	i--;
	j--;

	for (k = 2; k >= 0; k--) {
		for (l = 2; l >= 0; l--) {
			if (k && l) break;
			if (array[i + k][j + l] >= array[i][j]) return 0;
		}
	}

	return 1;
}

# ¿ Dec 21, 2010 23:09

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# ¿ May 17, 2024 13:47

icantfindaname: Jul 1, 2008

rjmccall posted:

It's the line with the break statement. First, break; doesn't do what I think you think it does, and second, you have the condition wrong.

What condition?

# ¿ Dec 22, 2010 00:04

icantfindaname: Jul 1, 2008

Alright, thanks, I got it to work now

icantfindaname fucked around with this message at 03:32 on Dec 22, 2010

# ¿ Dec 22, 2010 01:53

icantfindaname: Jul 1, 2008

Whoops, actually it compiles but doesn't display the

code:

printf ("%d in location (%d, %d)\n", array[i][j], i, j);

part, as if IsLarger never returns true

Any more insight?

Here's the program as it is now

code:

#include <stdio.h>
#include <stdlib.h>

#define SIZE 3

int IsLarger (int array[SIZE + 2][SIZE + 2], int i, int j);

int main ()
{
	int array[SIZE+2][SIZE+2], i, j;

	for (i = 0; i < SIZE + 2; i++) {
		for (j = 0; j < SIZE + 2; j++) {
			array[i][j] = -32766;
		}
	}

	for (i = 1; i <= SIZE; i++) {
		for (j = 1; j <= SIZE; j++) {
			printf("\nPlease enter an integer: ");
			scanf("%d", &array[i][j]);
		}
	}

	for (i = 1; i <= SIZE; i++) {
		for(j = 1; j <= SIZE; j++) {
			if (IsLarger(array, i, j) == 1) printf ("%d in location (%d, %d)\n", array[i][j], i, j);
		}
	}

	for (i = 1; i <= SIZE; i++) {
		for(j = 1; j <= SIZE; j++) {
			printf ("[%d]", array[i][j]);
		}
		printf("\n");
	}
	system("pause");
}

int IsLarger (int array[SIZE + 2][SIZE + 2], int i, int j)
{
	int k, l;
	i--;
	j--;

	for (k = 2; k >= 0; k--)
	{
		for (l = 2; l >= 0; l--)
		{
			if ((k != 1) && (l != 1)) {
				if (array[i + k][j + l] >= array[i][j]) return 0;
			}
		}
	}
	return 1;
}

# ¿ Dec 22, 2010 03:32

icantfindaname: Jul 1, 2008

I think I have this figured out. How would I express the condition !(both k and l are equal to zero)? (!(k && l == 0)) doesn't seem to be working

# ¿ Dec 22, 2010 07:43

icantfindaname: Jul 1, 2008

Thanks, it finally works now

# ¿ Dec 22, 2010 08:07

icantfindaname: Jul 1, 2008

Is there any easy way to concatenate a character to a string in C? Specifically, take a character out of another string, iterating through with a for loop. I tried strcat but apparently it needs to be a constant char for that to work. The program is supposed to check whether a string is a palindrome.

code:

for (i = StringLength (InputLine) - 1; i >= 0; i--) {
	if (!(StringEqual (CharToString(InputLine[i]), " "))) {
		//insert concat function here
	}
}

# ¿ Feb 23, 2011 05:20

icantfindaname: Jul 1, 2008

Alright, thanks

# ¿ Feb 23, 2011 05:45

icantfindaname: Jul 1, 2008

When I try to compile this code in visual c++ express 2010 on windows 7, it gives me a bunch of syntax errors on the brackets in the sort function:

code:

9    void sort (int *array1, int length)
10   {
11	     quick (array1, array1 + length - 1);
12   }
13
14   void quick (int *left, int *right)
15   {
16	     if (right > left) {
17		     int pivot = left [(right - left) / 2];
18		     int *r = right;
19		     int *l = left;
20
21		     while (1) {
22			     while (*l < pivot) l++;
23			     while (*r > pivot) r--;
24			     if (l <= r) {
25				     int t = *l;
26				     *l++ = *r;
27				     *r-- = t;
28			     }
29		     if (l > r) break;
30		     }
31
32		     quick (left, r);
33		     quick (l, right);
34	     }
35   }

The errors:

code:

1>quicksort.cpp(9): error C2143: syntax error : missing ')' before 'constant'
1>quicksort.cpp(9): error C2143: syntax error : missing ';' before 'constant'
1>quicksort.cpp(9): error C2059: syntax error : ')'
1>quicksort.cpp(10): error C2143: syntax error : missing ';' before '{'
1>quicksort.cpp(10): error C2447: '{' : missing function header (old-style formal list?)

There's probably a stupid reason but I can't see it, any help?

# ¿ Mar 22, 2011 03:10

icantfindaname: Jul 1, 2008

MutantBlue posted:

Those line numbers (9,10,11,...) aren't actually in your source file are they? I get similar errors if I don't edit out the line numbers.

I added them to show the lines in the error messages. On second thought, here's the whole program

code:

// quicksort.cpp : main project file.

#include "stdafx.h"
#include <stdio.h>
#include "simpio.h"

#define length 16

void sort (int *array1, int length)
{
	quick (array1, array1 + length - 1);
}

void quick (int *left, int *right)
{
	if (right > left) {
		int pivot = left [(right - left) / 2];
		int *r = right;
		int *l = left;

		while (1) {
			while (*l < pivot) l++;
			while (*r > pivot) r--;
			if (l <= r) {
				int t = *l;
				*l++ = *r;
				*r-- = t;
			}
		if (l > r) break;
		}

		quick (left, r);
		quick (l, right);
	}
}

int main (void)
{
	int i;

	int array1 [length];

	printf ("Enter %d elements seperately: ", length);

	for (i = 0; i < length; i++) {
		array1 [i] = GetInteger();
	}

	for (i = 0; i < length; i++) printf ("[%d]", array1[i]);
	printf ("\n");

	sort (array1, length);
	
	for (i = 0; i < length; i++) printf ("[%d]", array1[i]);
	printf ("\n");

	getchar ();
}

Sorry about that

# ¿ Mar 22, 2011 03:30

icantfindaname: Jul 1, 2008

nielsm posted:

It looks like it might be some kind of homework or other. The C standard library also has a qsort() function.

Yep, and thanks, it works now

# ¿ Mar 22, 2011 03:46

icantfindaname: Jul 1, 2008

So I have this basic file i/o program, but when it runs I get a segmentation fault (and also a compiler warning about exit()). I'm running x64 Ubuntu. What exactly is the problem? Both in.list and out.list exist and are in the same directory as the binary.

code:

#include <stdio.h>

int main(int argc, char **argv)
{
        FILE *ifp, *ofp;
        char outputFilename[] = "out.list";
        char username[9];
        int score;

        ifp = fopen("in.list", "r");

        if (ifp == NULL)
        {
                printf("Can't open input file in.list!\n");
                exit(1);
        }

        ofp = fopen("out.list", "w");

        if (ofp = NULL)
        {
                fprintf(stderr, "Can't open output file %s!\n", outputFilename);
                printf("DONGS");
                exit(1);
        }

        while (fscanf(ifp, "%s %d", username, &score) != EOF)
        {
                fprintf(ofp, "%s %d\n", username, score+10);
        }

        fclose(ofp);
        fclose(ifp);

        return 0;
}

edit: Including stdlib fixes the error, but the segmentation fault is still there.

icantfindaname fucked around with this message at 22:23 on Dec 22, 2012

# ¿ Dec 22, 2012 22:13

icantfindaname: Jul 1, 2008

b0lt posted:

Ah, that would do it. Thanks.

# ¿ Dec 22, 2012 22:26

icantfindaname: Jul 1, 2008

edit: Okay, I fixed the problem. But I'm still interested in what the problem actually was. The string behavior is loving bizarre: When I try to append one string to another it's just replacing the first X characters of the first string with the second. Removing the final character of the first string fixes it but what is that character doing even?

code:

#include <iostream>
#include <string>
#include <fstream>
#include <sstream>
#include "BinaryStringTree.h"

int main ()
{
        BinaryStringTree *tree = new BinaryStringTree();

        std::ifstream input;
        std::string line, first, last;
        input.open ("hash_short");

        if (input.is_open ()) {
                while (std::getline (input, line)) {
//                      std::cout << line << std::endl;

                        int i = 0;
                        while (i < line.size()) {
                                if (line[i] == '#') break;
                                i++;
                        }

                        last = line.substr (i + 1, std::string::npos);
                        first = line.substr (0, i + 1);


                        std::cout << first << std::endl << last << std::endl;

                        last.append (first);

                        std::cout << last << std::endl;

                        tree->insertNode (last);
                }

                input.close ();
        }



//      std::cout << "\nIn-order traversal of this tree: \n";
//      std::cout << std::endl;
//      tree->getInOrderTraversal (tree);
//      std::cout << std::endl;

        return 0;
}

Output:

code:

1, #
yapbozmeb
1, #ozmeb
2, #
gameinsight
2, #insight
3, #
android
3, #oid
4, #
rt
4, #
5, #
premiosgoya
5, #iosgoya
6, #
androidgames
6, #oidgames
7, #
goya2014
7, #2014
8, #
ipad
8, #
9, #
ipadgames
9, #games
10, #
birnesilgeliyor
10, #silgeliyor

icantfindaname fucked around with this message at 08:09 on Nov 26, 2015

# ¿ Nov 26, 2015 00:41

icantfindaname: Jul 1, 2008

I'm trying to write a program in C that parses a string containing 5 currencies and converts them to dollars, character by character with getchar(), so for example the input "$500�500�500�500₹500"

What I have works correctly except for a bizarre bug where the value after the amount in pounds always shows up zero, so the above input gives this output

code:

$500
$823 in sterling
$0 in yen
$683 in euros
$8 in rupees

The input $500�500$500 gives

code:

$500
$823 in sterling
$0

My code is this. I use a C string to hold the characters grabbed from stdin before converting them to an integer, and if you print the raw string containing the characters supposed to be $500 in the above it's super hosed up, the characters themselves seem to be random numbers. What the heck is the problem?

code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char * append(char *str, char c)
{
        size_t len = strlen(str);
	char *str2 = malloc(len + 1 + 1);
	strcpy(str2, str);
        str2[len] = c;
        str2[len+1] = '\0';
	free(str);
	return str2;
}

int main ()
{
	int n, total = 0;
	char *str = malloc(sizeof(char));

	printf("Please enter a sum of money in sterling, yen, rupees or euros: ");

	for (int c = getchar(); c != '\n' && c != EOF; c = getchar()) {

		if (c == 0x24) {
			while ((c = getchar()) != '\n' && c != EOF) {
				if (c == 0xC2 || c == 0xE2) { ungetc(c, stdin); break; }

				str = append(str, c);
			}

			n = atoi(str);

			printf("%d %d %d\n", str[0], str[1], str[2]);

			printf("$%d\n", n);

			total += n;

			free(str);

			str = malloc(sizeof(char));

			continue;

		}

		if (c == 0xC2) {
			c = getchar();
			if (c == 0xA3) {
				while ((c = getchar()) != '\n' && c != EOF) {
					if (c == 0x24 || c == 0xE2 || c == 0xC2) { ungetc(c, stdin); break; }

					str = append(str, c);
				}

				n = atoi(str);

				n = n * 1000 / 607;

				printf("$%d in sterling\n", n);

				total += n;

        	                free(str);

     	           	        str = malloc(sizeof(char));

				continue;
			}

                        if (c == 0xA5) {
                                while ((c = getchar()) != '\n' && c != EOF) {
                                        if (c == 0x24 || c == 0xE2 || c == 0xC2) { ungetc(c, stdin); break; }

                                        str = append(str, c);
                                }

                                n = atoi(str);

                                n = n * 100 / 10404;

                                printf("$%d in yen\n", n);

                                total += n;

				str = malloc(sizeof(char));

				continue;
                        }

		}

		if (c == 0xE2) {
                        c = getchar();
			c = getchar();
                        if (c == 0xAC) {
                                while ((c = getchar()) != '\n' && c != EOF) {
                                        if (c == 0x24 || c == 0xC2 || c == 0xE2) { ungetc(c, stdin); break; }

                                        str = append(str, c);
                                }

                                n = atoi(str);

                                n = n * 1000 / 732;

                                printf("$%d in euros\n", n);

                                total += n;

				str = malloc(sizeof(char));

				continue;
                        }

                        if (c == 0xB9) {
                                while ((c = getchar()) != '\n' && c != EOF) {
                                        if (c == 0x24 || c == 0xC2 || c == 0xE2) { ungetc(c, stdin); break; }

                                        str = append(str, c);
                                }

                                n = atoi(str);

                                n = n * 1000 / 61903;

                                printf("$%d in rupees\n", n);

                                total += n;

				str = malloc(sizeof(char));

				continue;
                        }

		}
	} 

	

	free(str);

	return 0;

}

# ¿ Dec 29, 2016 02:58

icantfindaname: Jul 1, 2008

Joda posted:

Don't you need to use wide characters to read your input for �/�/�/₹ since they don't exist in ASCII?

Yeah, those characters exist as multiple characters in stdin, you can use multiple getchar() calls to pull them out. ₹ is 0xE2, 0x82, 0xB9

That's not the problem though, it works fine except after a pounds-denominated value

# ¿ Dec 29, 2016 03:41

icantfindaname: Jul 1, 2008

Dylan16807 posted:

You're not initializing str when you malloc it. That could cause all sorts of weirdness.

If I set the value of the pointer with strcpy(str, " "); it still gives the error

# ¿ Dec 29, 2016 23:45

icantfindaname: Jul 1, 2008

Okay, the problem was in the dynamic allocation of memory for the holder string. Man, memory management is a nightmare

# ¿ Dec 30, 2016 04:51

icantfindaname: Jul 1, 2008

I�m trying to do these SDL tutorials in Ubuntu and the programs won�t compile, when I try to compile this file it gives this error

https://lazyfoo.net/tutorials/SDL/15_rotation_and_flipping/index.php

https://pastebin.com/HsGLyTEh

code:

VirtualBox:~/sdl/tutorial6/15_rotation_and_flipping$ gcc 15_ro    tation_and_flipping.cpp -w -lSDL2 -lSDL2_image -I/usr/local/include/SDL2 -D_REEN    TRANT
/usr/bin/ld: /tmp/ccldwsPN.o: in function `LTexture::loadFromFile(std::__cxx11::    basic_string<char, std::char_traits<char>, std::allocator<char> >)':
15_rotation_and_flipping.cpp:(.text+0x81): undefined reference to `std::__cxx11:    :basic_string<char, std::char_traits<char>, std::allocator<char> >::c_str() cons    t'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0xa8): undefined reference to `    std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >:    :c_str() const'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x12b): undefined reference to     `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >    ::c_str() const'
/usr/bin/ld: /tmp/ccldwsPN.o: in function `loadMedia()':
15_rotation_and_flipping.cpp:(.text+0x4f8): undefined reference to `std::allocat    or<char>::allocator()'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x50f): undefined reference to     `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >    ::basic_string(char const*, std::allocator<char> const&)'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x533): undefined reference to     `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >    ::~basic_string()'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x53f): undefined reference to     `std::allocator<char>::~allocator()'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x57b): undefined reference to     `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >    ::~basic_string()'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x590): undefined reference to     `std::allocator<char>::~allocator()'
/usr/bin/ld: /tmp/ccldwsPN.o:(.data.rel.local.DW.ref.__gxx_personality_v0[DW.ref    .__gxx_personality_v0]+0x0): undefined reference to `__gxx_personality_v0'
collect2: error: ld returned 1 exit status

Some research says this might be caused by the SDL libraries being compiled with a different version of GCC, but I reinstalled SDL from source and it still gives the same exact error

Specifying std=c++11 does not help either

icantfindaname fucked around with this message at 02:39 on Feb 10, 2021

# ¿ Feb 10, 2021 02:36

icantfindaname: Jul 1, 2008

Now I�m getting this error. I have the packages for libsdl2-image and libsdl2-image-dev both installed, but it doesn�t seem to recognize them. There is indeed a prototype for IMG_Load() in /usr/include/SDL2/SDL_image.h

https://pastebin.com/eiEkCJ8E

code:

VirtualBox:~/SDL/tutorial15/15_rotation_and_flipping$ g++ -lSDL2 -lSDL2_image -I/usr/include/SDL2 -D_REENTRANT 15_rotation_and_flipping.cpp
/usr/bin/ld: /tmp/ccxrAWJZ.o: in function `LTexture::loadFromFile(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)':
15_rotation_and_flipping.cpp:(.text+0x89): undefined reference to `IMG_Load'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x99): undefined reference to `SDL_GetError'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0xe3): undefined reference to `SDL_MapRGB'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0xf6): undefined reference to `SDL_SetColorKey'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x10c): undefined reference to `SDL_CreateTextureFromSurface'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x11c): undefined reference to `SDL_GetError'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x16c): undefined reference to `SDL_FreeSurface'
/usr/bin/ld: /tmp/ccxrAWJZ.o: in function `LTexture::free()':
15_rotation_and_flipping.cpp:(.text+0x1b7): undefined reference to `SDL_DestroyTexture'
/usr/bin/ld: /tmp/ccxrAWJZ.o: in function `LTexture::setColor(unsigned char, unsigned char, unsigned char)':
15_rotation_and_flipping.cpp:(.text+0x214): undefined reference to `SDL_SetTextureColorMod'
/usr/bin/ld: /tmp/ccxrAWJZ.o: in function `LTexture::setBlendMode(SDL_BlendMode)':
15_rotation_and_flipping.cpp:(.text+0x23f): undefined reference to `SDL_SetTextureBlendMode'
/usr/bin/ld: /tmp/ccxrAWJZ.o: in function `LTexture::setAlpha(unsigned char)':
15_rotation_and_flipping.cpp:(.text+0x26c): undefined reference to `SDL_SetTextureAlphaMod'
/usr/bin/ld: /tmp/ccxrAWJZ.o: in function `LTexture::render(int, int, SDL_Rect*, double, SDL_Point*, SDL_RendererFlip)':
15_rotation_and_flipping.cpp:(.text+0x310): undefined reference to `SDL_RenderCopyEx'
/usr/bin/ld: /tmp/ccxrAWJZ.o: in function `init()':
15_rotation_and_flipping.cpp:(.text+0x36d): undefined reference to `SDL_Init'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x379): undefined reference to `SDL_GetError'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x3a9): undefined reference to `SDL_SetHint'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x3ea): undefined reference to `SDL_CreateWindow'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x402): undefined reference to `SDL_GetError'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x438): undefined reference to `SDL_CreateRenderer'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x450): undefined reference to `SDL_GetError'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x48e): undefined reference to `SDL_SetRenderDrawColor'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x49f): undefined reference to `IMG_Init'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x4b0): undefined reference to `SDL_GetError'
/usr/bin/ld: /tmp/ccxrAWJZ.o: in function `close()':
15_rotation_and_flipping.cpp:(.text+0x5cc): undefined reference to `SDL_DestroyRenderer'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x5db): undefined reference to `SDL_DestroyWindow'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x5f6): undefined reference to `IMG_Quit'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x5fb): undefined reference to `SDL_Quit'
/usr/bin/ld: /tmp/ccxrAWJZ.o: in function `main':
15_rotation_and_flipping.cpp:(.text+0x685): undefined reference to `SDL_PollEvent'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x74d): undefined reference to `SDL_SetRenderDrawColor'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x75c): undefined reference to `SDL_RenderClear'
/usr/bin/ld: 15_rotation_and_flipping.cpp:(.text+0x7d3): undefined reference to `SDL_RenderPresent'
collect2: error: ld returned 1 exit status

# ¿ Feb 10, 2021 04:44

icantfindaname: Jul 1, 2008

Okay, I got it working by changing the order around, thanks

icantfindaname fucked around with this message at 05:38 on Feb 10, 2021

# ¿ Feb 10, 2021 05:35

icantfindaname: Jul 1, 2008

I'm trying to write mods/change code in nethack, I have built it successfully on ubuntu, but what is the process of rebuilding it after I have edited the source code? Just do make install again?

https://github.com/NetHack/NetHack

# ¿ Mar 16, 2024 02:04

icantfindaname: Jul 1, 2008

So it will just replace the existing binaries in /usr/local/bin?

# ¿ Mar 16, 2024 02:51

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# ¿ May 17, 2024 13:47

icantfindaname: Jul 1, 2008

Alright, thanks

# ¿ Mar 16, 2024 23:20

The Something Awful Forums > Discussion > Serious Hardware/Software Crap > The Cavern of COBOL > C/C++ Programming Questions Not Worth Their Own Thread