For my OS class, I need to print out the result of this matrix multiplication using only system calls. Following my lecture notes, I wrote up this piece of code. I use :
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define N 1000
// Matrix
long long int A[N][N],B[N][N],R[N][N];
int main(int argc, char *argv[])
{
int x,y,z;
char str[100];
/* Matrix inicialization */
for(y=0;y<N;y++)
for(x=0;x<N;x++)
{
A[y][x]=x;
B[y][x]=y;
R[y][x]=0;
}
/* Matrix multiplication */
for(y=0;y<N;y++)
for(z=0;z<N;z++)
for(x=0;x<N;x++)
{
R[y][x]+= A[y][z] * B[z][x];
}
//System calls for printing the result
sprintf(str,"%lld\n",R);
write(1,str,strlen(str));
exit(0);
}
Now, it's printing a just a 14295680 in the console. The professor gave us a file with machine code and it's printing 332833500, which seems more reasoneable.
Thanks in advance.
Edit: changed type on the printf call
Edit2: fix R[N][N]
Just replace the sprintf value:
sprintf(str,"%lld\n",R[N-1][N-1]); // = 332833500
write(1,str,strlen(str));
instead of
sprintf(str,"%lld\n",R); // this is a pointer
write(1,str,strlen(str));
Related
I need help to understand why in this little program i cannot manipulate correctly pointers:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void change(char *s[][15]){
int i=0;
while(i<5){
if(s[i][0]=='B') s[i][0]='v';
i++;
}
}
/*My code is supposed to allocate dynamically 5 arrays of 15 chars each
(like tab[5][15])and then put a message on them and try to modify the messages.
In this particular case i'm trying to change the first letter of each string to 'V'.
I'm doing this little experience because of another program
in which i have difficulties accessing double arrays*/
int main(){
int i;
char **s;
s =malloc(5*sizeof(char*));
for(i=0;i<5;i++){
s[i]=malloc(15*sizeof(char));
sprintf(s[i],"Bonjour%d",i);
}
change(s);
for(i=0;i<5;i++){
printf("%s\n",s[i]);
}
return 0;
}
I was expecting :
Vonjour0
Vonjour1
Vonjour2
Vonjour3
Vonjour4
but I get :
Bonjour0
Bonjour1
Bonjour2
Bonjour3
Bonjour4
I'm testing this little code for another program and I don't get why the arrays don't change.
In my other program I can't access the double pointer or print the content.
so my question is : why in this program I can't modify the content of the arrays ?
Your change method needs to use "char** s" instead of char *s[][15]. This is because your method is expecting a pointer to a multi-dimensional array. This is immutable as a result, since your original data type for the string is a pointer to an array of strings (IE: An array of chars).
Hopefully that was clear.
It should be
char **change(char **s){
int i=0;
while(i<5){
if(s[i][0]=='B') s[i][0]='v';
i++;
}
return s;
}
You only need to change the function argument to char *s[].
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void change(char *s[]){
int i=0;
while(i<5){
if(s[i][0]=='B') s[i][0]='v';
i++;
}
}
int main(){
int i;
char **s;
s =malloc(5*sizeof(char*));
for(i=0;i<5;i++){
s[i]=malloc(15*sizeof(char));
sprintf(s[i],"Bonjour%d",i);
}
change(s);
for(i=0;i<5;i++){
printf("%s\n",s[i]);
}
return 0;
}
Program output:
vonjour0
vonjour1
vonjour2
vonjour3
vonjour4
I want to do a code that searches a txt file and returns the number of different words and how many times they appear on the text.
I' trying to do that, but I'm having a problem on comparing the word read from the input with the words already read. So I'm doing a code that adds a word to the vector of words if is new, and if it isn't, it increments by 1 the word count. But when I'm comparing the words, it doesn't states that they're equal even when they aren't.
By exemple: txt is filled with:
test test test.
test test test.
("test." =/= from "test"). And it return 7 different words with 3 being NULL, "3 test" and 1 "test." . That should return 2 words and count 4 on test and count 2 on test.
Can anybody see what is wrong with my code?
#define MAX_PALAVRAS 1024
#define MAX_TAM_PALAVRA 32
typedef struct ocorrencia_ {
char palavra[MAX_TAM_PALAVRA];
int pos;
int num_ocorrencias;
}ocorrencia;
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
int main (int argc, char * argv[]){
ocorrencia palavras[MAX_PALAVRAS];
int i,palavras_diferentes=0,palavra_atual=0;
char aux[MAX_TAM_PALAVRA];
bool nova_palavra=true;
for (i=0;i<MAX_PALAVRAS;i++){
palavras[i].pos=-1;
palavras[i].num_ocorrencias=0;
}
FILE * D = fopen("input.txt","r");
while (!feof(D)){
char aux2[MAX_TAM_PALAVRA];
fscanf(D,"%s",aux);
for (i=0;i<palavras_diferentes;i++){
if (strcmp(palavras[palavras_diferentes].palavra,aux)==0){
nova_palavra=false;
break;
}
palavra_atual++;
}
if (nova_palavra){
strcpy(palavras[palavra_atual].palavra,aux);
palavras_diferentes++;
}
palavras[palavra_atual].num_ocorrencias++;
printf("%s\n",palavras[palavra_atual].palavra);
}
fclose (D);
printf("diferent words=%i\n",palavras_diferentes);
printf("success!\n");
return (EXIT_SUCCESS);
}
Thanks for taking or time reading or trying to help!
Following my comments, here are a few changes that may help you :
-Set palavra_atual to 0 and nova_palavra to true at the beginning of the while loop.
-Test the return of fscanf, add something like if(fscanf(D,"%s",aux)==1){...}
-Test all words ! if (strcmp(palavras[i].palavra,aux)==0)
Here goes the code :
#define MAX_PALAVRAS 1024
#define MAX_TAM_PALAVRA 32
typedef struct ocorrencia_ {
char palavra[MAX_TAM_PALAVRA];
int pos;
int num_ocorrencias;
}ocorrencia;
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
int main (int argc, char * argv[]){
ocorrencia palavras[MAX_PALAVRAS];
int i,palavras_diferentes=0,palavra_atual=0;
char aux[MAX_TAM_PALAVRA];
bool nova_palavra=true;
for (i=0;i<MAX_PALAVRAS;i++){
palavras[i].pos=-1;
palavras[i].num_ocorrencias=0;
}
FILE * D = fopen("input.txt","r");
while (!feof(D)){
palavra_atual=0;
nova_palavra=true;
char aux2[MAX_TAM_PALAVRA];
if(fscanf(D,"%s",aux)==1){
for (i=0;i<palavras_diferentes;i++){
if (strcmp(palavras[i].palavra,aux)==0){
nova_palavra=false;
break;
}
palavra_atual++;
}
if (nova_palavra==true){
printf("new word %d %s\n",palavra_atual,aux);
strcpy(palavras[palavra_atual].palavra,aux);
palavras_diferentes++;
}
palavras[palavra_atual].num_ocorrencias++;
printf("%s\n",palavras[palavra_atual].palavra);
}
}
fclose (D);
printf("diferent words=%i\n",palavras_diferentes);
printf("success!\n");
return (EXIT_SUCCESS);
}
You will be interesseted by ispunct() of ctypes.h here
I am new with threads.
I am trying to make a C program that reverses the string given from the command line and create a thread that does this for each one . When I run it gives me Segmentation fault .
Here is the code:
#include <stdio.h>
#include <sys/types.h>
#include <pthread.h>
#include <stdlib.h>
#include <fcntl.h>
char* final[1000];
pthread_mutex_t *mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_t p[];
void *reverse(void* arg){
char* s[100];
char* temp;
int i;
strcpy(s,(char*)arg);
printf("S este %s",s);
for(i=0;i<=strlen(s)/2;i++){
strcpy(temp,s[i]);
strcpy(s[i],s[strlen(s)-i-1]);
strcpy(s[strlen(s)-i-1],temp);
}
sleep(1);
pthread_mutex_lock(&mutex);
strcat(final,s);
printf("Intermediar %s",s);
pthread_mutex_unlock(&mutex);
return NULL;
}
int main(int argc,char* argv[]) {
int i;
int n = argc;
strcpy(final,"");
for(i=1;i<n-2;i++){
pthread_create(&p[i],NULL,reverse,argv[i]);
}
for(i=1;i<n-2;i++){
pthread_join(p[i],NULL);
}
//printf("Sirul final este %s",final);
return 0;
}
Does anyone know a good site that could help me learn threads ?
Thanks !
char* final[1000];
is an array (with 1000 elements) of pointer to char, you want an array of char:
char final[1000];
the same problem with this array:
char* s[100];
temp is declared as a pointer, but you use it as an array with size 1
declare the mutex without the * ,remove the initialization and add in main:
pthread_mutex_init(&mutex, NULL);
you should also add a number to the array definition of pthread_t
You never initialize temp, so the call strcpy(temp, s[i]); causes undefined behavior.
Your treatment of s is also very confusing, the copying of arg (a string) into the memory used by s (an array of string pointers) is not valid. Just because you can cast away a warning doesn't mean you're doing something sensible.
i have the following problems in C programming.
I have an array of strings stored as words[10][50]. I want to extract each of the string from the array and then pass it on to another function. I tried on the following:
#include "stdafx.h"
#include "stdio.h"
#include "conio.h"
#include "stdlib.h"
int Check_Anagram(char*,char*);
void main()
{
char words[10][20];
int i;
int flag;
for(i=0;i<3;i++)
{
scanf("%s\n",words[i][20]);
}
for(i=1;i<10;i++)
{
flag = Check_Anagram(words[i][20],words[i-1][20]);
}
getch();
}
int Check_Anagram(char *a,char *b)
{
printf("%s %s\n",a,b);
return 1;
}
This creates an exception during compiling.
Now i think that when i use the "printf" statement then this nomenclature works fine i.i words[i] prints the string "i" from the double dimension words array. When i try to do the same thing with the check function then the error occurs.
Can soemone point me how to do this passing ?
P.S. Please ignore any error in efficiency of program and likewise. I need your help and this is just a test program at learning string passing to a function
Thanks
You're passing words[i][20]. You need to pass words[i] instead in both loops. Try this:
for(i = 1; i < 3; i++) /* i < 3 */
{
flag = Check_Anagram(words[i], words[i-1]);
}
Another problem is that you're reading 3 strings and trying to print 10. So when you pass words[3] it contains garbage: printf tries to print garbage which need not be 0-terminated.
In the first for loop, when i is 0, you're pointing to words[-1], that's your exception.
flag = Check_Anagram(words[i][20],words[i-1][20]);
You are passing the 21st letter of each word the Check_Anagram. Instead you should pass the words themselves:
flag = Check_Anagram(words[i],words[i-1]);
You have a similar problem where you use scanf. To read a line from the console to each word you would use:
for(i=0;i<10;i++)
{
scanf("%s\n",words[i]);
}
#include "stdafx.h"
#include "stdio.h"
#include "conio.h"
#include "stdlib.h"
int Check_Anagram(char [],char []);
void main()
{
char words[10][20];
int i;
int flag;
for(i=0;i<3;i++)
{
scanf("%s\n",words[i]);
}
for(i=1;i<10;i++)
{
flag = Check_Anagram(words[i],words[i-1]);
}
getch();
}
int Check_Anagram(char a[],char b[])
{
printf("%s %s\n",a,b);
return 1;
}
I finally got it corrected thanks to the help of all users.
I have posted the corrected code for people who are struggling with passing of string extracted from an array of strings to another function. hope it helps.
While reading a book called "Let us C" I read that a function showbit() exists which can show you the bits of the number. There wasn't any special header file mentioned for it. Searched for it on the internet and didn't found anything useful. Is there such a function? I want this to print the binary of decimal numbers. Else please give me a replacement function. Thanks
All integers are actually in binary in your computer. Its just that it is turned into a string that is the decimal representation of that value when you try to print it using printf and "%d". If you want to know what it looks like in some other base (e.g. base 2 or binary), you either have to provide the proper printf format string if it exists (e.g. "%x" for hex) or just build that string yourself and print it out.
Here is some code that can build the string representation of an integer in any base in [2,36].
#include <stdio.h>
#include <string.h>
char digits[]="01234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ";
void reverse(char* start, char* end)
{
for(end--;start<end;start++,end--)
{
char t=*start;
*start=*end;
*end=t;
}
}
int base_change(int n, int base,char* buffer)
{
int pos=0;
if (base>strlen(digits))
return -1;
while(n)
{
buffer[pos]=digits[n%base];
n/=base;
pos++;
}
buffer[pos]='\0';
reverse(buffer,buffer+pos);
return 0;
}
int main()
{
char buffer[32];
int conv=base_change(1024,2,buffer);
if (conv==0) printf("%s\n",buffer);
return 0;
}
You can also try this snippet which uses bit-shifting:
EDIT: (I've made it more portable)
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define BITS_IN_BYTE 8
#define INTEGRAL_TYPE unsigned int
void showBits(INTEGRAL_TYPE x) {
int i;
static int intSizeInBits = sizeof(INTEGRAL_TYPE) * BITS_IN_BYTE;
static char symbol[2] = {'0','1'};
char * binary = (char*) malloc(intSizeInBits + 1);
memset(binary, 0, intSizeInBits + 1);
for (i=0; i< intSizeInBits; i++) {
binary[intSizeInBits-i-1] = symbol[(x>>i) & 0x01];
}
printf("%s\n", binary);
free(binary);
}
int main() {
showBits(8698513);
return 0;
}
HTH!
This is a very simple solution for printing the bits of an integer
int value = 14;
int n;
for (n=8*sizeof(int)-1;n>=0;n--) {
printf("%d",(value >>n)&1);
}
The book "Let Us C" doesn't define it as a built-in function. The showbits() function is defined in later part of the book as a complete user defined function as I personally went through it. This answer is to anyone who haven't reached that later part of the book and are stuck at the first appearance of the function in the book.
you need to look here
#downvoter It works fine in c also. You just need to reformat your code in c-style.
#include <stdlib.h>
#include <stdio.h>
int main()
{
char buffer[20];
int i = 3445;
_itoa( i, buffer, 2 );
printf("String of integer %d (radix 2): %s",i,buffer);
return 0;
}
*you need to save your file as .c in MSVC++ for _itoa() to work.*
this is the header file for showbits
void showbits(unsigned int x)
{
int i;
for(i=(sizeof(int)*5)-1; i>=0; i--)
(x&(1u<<i))?putchar('1'):putchar('0');
printf("\n");
}
No there is no pre built function and you do not need to include any specific header file.
You will have to provide implementation for function showbits(int).
#include <stdio.h>
void showbits(int);
int main()
{
int j,k;
for(j=0;j<=11;j++)
{
printf("\nBinary value of decimal %d is :",j);
showbits(j);
}
return 0;
}
showbits(int n){
int i,k,andmask;
for(i = 15;i>=0;i--){
andmask = 1<<i;
k = n & andmask;
k==0 ? printf("0"):printf("1");
}
}
If you want to print out the bits of a float, for example you could do something like:
float myFloat = 45.2;
for (int n=0;n<8*sizeof(float);n++) {
printf("%d",(myFloat>>n)&1);
}