I have an issue with my Arduino. I am trying to convert a boolean array into an int with this piece of code:
int boolean_to_decimal(bool bol[]) {
int somme=0;
for (int i = 0; i < 6; i++){
somme += bol[i] * pow(2, 5-i);
}
return somme;
}
Nothing really impressive but here are my results:
010101 == 20 (instead of 21)
100101 == 36 (instead of 37)
101001 == 40 (instead of 41)
011001 == 23 (instead of 25)
etc
Thank you for your time, David
Using floating-point function pow() for integers seems bad because it may contain errors. Try using bit-shifting instead.
int boolean_to_decimal(bool bol[]){
int somme=0;
for (int i = 0; i<6; i++){
somme += bol[i]*(1 << (5-i));
}
return somme;
}
Related
I have an arudino code where I get some temperature reading:
double c1 = device.readCelsius();
Serial.println(c1);
The output is for example: 26.23
What I need is to get this converted to 2623 and then to HEX value so I get: 0x0A3F
Any clue?
I guess your float values always get numbers up to two decimal. So, you can just multiply the value which you read from sensor with a 100.
decimalValue = 100 * c1
And then you can use this small code for converting the decimal value to HEX.
Thanks to GeeksforGeeks
You can find the full tutorial here
// C++ program to convert a decimal
// number to hexadecimal number
#include <iostream>
using namespace std;
// function to convert decimal to hexadecimal
void decToHexa(int n)
{
// char array to store hexadecimal number
char hexaDeciNum[100];
// counter for hexadecimal number array
int i = 0;
while (n != 0) {
// temporary variable to store remainder
int temp = 0;
// storing remainder in temp variable.
temp = n % 16;
// check if temp < 10
if (temp < 10) {
hexaDeciNum[i] = temp + 48;
i++;
}
else {
hexaDeciNum[i] = temp + 55;
i++;
}
n = n / 16;
}
// printing hexadecimal number array in reverse order
for (int j = i - 1; j >= 0; j--)
cout << hexaDeciNum[j];
}
// Driver program to test above function
int main()
{
int n = 2545;
decToHexa(n);
return 0;
}
Why do I get a segfault when I try to print the strlen of a string, which is part of an array of strings? I can print each string - the printf works perfectly. But why does the strlen cause a segfault?
The below program first takes an input n, which is the number of strings I want to dynamically allocate. Then I allocate space for 32 bytes for each string
int main() {
int i;
int n;
char **nums;
scanf("%d", &n);
printf("n = %d\n", n);
nums = malloc(sizeof(char *) * n);
printf("allocated nums\n");
for(i=0; i<n; i++) {
nums[i] = malloc(sizeof(char) * 32);
memset(nums[i], '\0', sizeof(char) * 32);
}
for(i=0; i < n; i++) {
scanf("%s", &nums[i]);
}
for(i=0; i<n; i++) {
// THIS PRINTS FINE
printf("string = %s\n", &nums[i]);
// SEGFAULT HERE IMMEDIATELY
printf("length = %d\n", strlen(nums[i]));
}
Here is the console output. As a test, I entered in n=3, followed by the numbers 45, 46, and 47:
3
n = 3
allocated nums
45
46
47
string = 45
Segmentation fault (core dumped)
Additionally, I get a segfault when I try to access an individual character in each string. Again, the first printf in outer for loop prints the string, then I get a segfault accessing nums[i][k]:
int i, k=0;
for(i=0; i<n; i++) {
printf("Printiiing: %s\n", &nums[i]);
// WHY DOES THIS SEGFAULT???
//printf("first char = %c\n", nums[i][0]);
while(k<32 && nums[i][k] != '\0') {
// THIS CAUSES A SEG FAULT
printf("char = %c", (nums[i])[k]);
k++;
}
}
This is fine:
for(i=0; i<n; i++) {
nums[i] = malloc(sizeof(char) * 32);
memset(nums[i], '\0', sizeof(char) * 32);
}
After this loop, each nums[i] is a pointer to 32-byte buffer.
But this corrupts (overwrites) all the pointers, instead of reading strings into the allocated buffers:
for(i=0; i < n; i++) {
scanf("%s", &nums[i]);
}
To fix the bug, use: scanf("%s", nums[i]);.
There is the difference pointer between the &nums[i] and nums[i] address. You can check with the strlen((const char*)(&nums[i])) for get length.
The explanation of #Employee of Russia is exactly for reason.
I am trying to perform a backward slicing of an array element at specific position. I tried two different source codes. The first one is (first.c):
const int in_array[5][5]={
1,2,3,4,5,
6,7,8,9,10,
11,12,13,14,15,
16,17,18,19,20,
21,22,23,24,25
};
int out_array[5][5];
int main(unsigned int x, unsigned int y)
{
int res;
int i;
int j;
for(i=0; i<5; i++){
for(j=0; j<5; j++){
out_array[i][j]=i*j*in_array[i][j];
}
}
res = out_array[x][y];
return res;
}
I run the command:
frama-c-gui -slevel 10 -val -slice-return main file.c
and get the following generated code:
int main(unsigned int x, unsigned int y)
{
int res;
int i;
int j;
i = 0;
while (i < 5) {
j = 0;
while (j < 5){
out_array[i][j] = (i * j) * in_array[i][i];
j ++;
}
i ++;
}
res = out_array[x][y];
return res;
}
This seems to be ok, since the x and y are not defined, so the "res" can be at any position in the out_array. I tried then with the following code:
const int in_array[5][5]={
1,2,3,4,5,
6,7,8,9,10,
11,12,13,14,15,
16,17,18,19,20,
21,22,23,24,25
};
int out_array[5][5];
int main(void)
{
int res;
int i;
int j;
for(i=0; i<5; i++){
for(j=0; j<5; j++){
out_array[i][j]=i*j*in_array[i][j];
}
}
res = out_array[3][3];
return res;
}
The result given was exactly the same. However, since I am explicitly looking for a specific position inside the array, and the loops are independent (parallelizable), I would expect the output to be something like this:
int main(void)
{
int res;
int i;
int j;
i = 3;
j = 3;
out_array[i][j]=(i * j) * in_array[i][j];
res = out_array[3][3];
}
I am not sure if is it clear from the examples. What I want to do is to identify, for a given array position, which statements impact its final result.
Thanks in advance for any support.
You obtain "the statements which impact the final result". The issue is that not all loop iterations are useful, but there is no way for the slicing to remove a statement to the code in its current form. If you perform syntactic loop unrolling, with -ulevel 5, then you will each loop iteration is individualized, and slicing can decide for each of them whether it is to be included in the slice or not. In the end, frama-c-gui -ulevel 5 -slice-return main loop.c gives you the following code
int main(void)
{
int res;
int i;
int j;
i = 0;
i ++;
i ++;
i ++;
j = 0;
j ++;
j ++;
j ++;
out_array[i][j] = (i * j) * in_array[i][j];
res = out_array[3][3];
return res;
}
which is indeed the minimal set of instructions needed to compute the value of out_array[3][3].
Of course whether -ulevel n scales up to very high values of n is another question.
I'm trying to take to the following input:
1
4
47 2 4 43577
The part of my code that deals with this is:
for (scanf("%d", &t); t --; )
{
int count = 0;
scanf("%d",&n);
for (int i = 0, x; i < n; ++ i)
{
scanf("%d",&x);
str = to_string(x);
f4[i] = get_count(str,'4');
f7[i] = get_count(str,'7');
}
However, with this I get a runtime error, which shows an access violation in the file free.c.
But, when I try to debug it, it runs well in the debug mode and gives the correct answer.
Also, when I output the variable x right after I input it, the program works well in runtime as well. This is shown in the following code, which runs fine in runtime as well:
for (scanf("%d", &t); t --; )
{
int count = 0;
scanf("%d",&n);
for (int i = 0, x; i < n; ++ i)
{
scanf("%d",&x);
cout<<"A"<<i<<" is "<<x<<'\n';
str = to_string(x);
f4[i] = get_count(str,'4');
f7[i] = get_count(str,'7');
}
Any idea why this may be happening?
Some of the stackoverflow users are saying that the code runs fine. I'm using VS 2012. Can this be something that is compiler specific?
The complete code:
#include<iostream>
#include<conio.h>
#include<string>
#include<math.h>
using namespace std;
int get_count(string s, char x)
{
int count = 0;
int l = s.length();
for(int i = 0; i < l;i++)
{
if (s[i] == x)
count++;
}
return count;
}
void main()
{
int * f4 = new int;
int * f7 = new int;
string * back = new string;
int n = 0;
int t = 0;
string str;
for (scanf("%d", &t); t --; )
{
int count = 0;
scanf("%d",&n);
for (int i = 0, x; i < n; ++ i)
{
scanf("%d",&x);
str = to_string(x);
f4[i] = get_count(str,'4');
f7[i] = get_count(str,'7');
}
for(int i = 0;i < n;i++)
{
for(int j = i; j < n;j++)
{
int c4 = 0;
int c7 = 0;
for(int k = i; k <= j;k++)
{
c4 += f4[k];
c7 += f7[k];
}
double value = pow((double)c4,(double)c7);
if(value <= (double)(j - i + 1)&&(c4!=2)&&(c7!=2))
{
count++;
//cout<<"yes"<<'\t';
}
}
}
cout<<"Ans: "<<count<<'\n';
}
//getch();
}
There are no other variable assignments apart from those in this code.
The exact error that I get with runtime is:
Unhandled exception at 0x7794E3BE (ntdll.dll) in Practice1.exe: 0xC0000005: Access violation reading location 0x38389246.
You did not include the "get_count" function. I think it has something to do with that function. I rewrote that function to return some number and I don't get that error. Try to assert that you are not attempting to use a null pointer in that function.
Works fine on my machine:
Here's what I changed
for (int i = 0, x; i < n; ++ i)
{
scanf("%d",&x);
stringstream ss;
ss << x;
str = ss.str();
f4[i] = get_count(str,'4');
f7[i] = get_count(str,'7');
}
Output:
1
4
47 2 4 43577
Ans: 5
Have you tried the latest Codility test?
I felt like there was an error in the definition of what a K-Sparse number is that left me confused and I wasn't sure what the right way to proceed was. So it starts out by defining a K-Sparse Number:
In the binary number "100100010000" there are at least two 0s between
any two consecutive 1s. In the binary number "100010000100010" there
are at least three 0s between any two consecutive 1s. A positive
integer N is called K-sparse if there are at least K 0s between any
two consecutive 1s in its binary representation. (My emphasis)
So the first number you see, 100100010000 is 2-sparse and the second one, 100010000100010, is 3-sparse. Pretty simple, but then it gets down into the algorithm:
Write a function:
class Solution { public int sparse_binary_count(String S,String T,int K); }
that, given:
string S containing a binary representation of some positive integer A,
string T containing a binary representation of some positive integer B,
a positive integer K.
returns the number of K-sparse integers within the range [A..B] (both
ends included)
and then states this test case:
For example, given S = "101" (A = 5), T = "1111" (B=15) and K=2, the
function should return 2, because there are just two 2-sparse integers
in the range [5..15], namely "1000" (i.e. 8) and "1001" (i.e. 9).
Basically it is saying that 8, or 1000 in base 2, is a 2-sparse number, even though it does not have two consecutive ones in its binary representation. What gives? Am I missing something here?
Tried solving that one. The assumption that the problem makes about binary representations of "power of two" numbers being K sparse by default is somewhat confusing and contrary.
What I understood was 8-->1000 is 2 power 3 so 8 is 3 sparse. 16-->10000 2 power 4 , and hence 4 sparse.
Even we assume it as true , and if you are interested in below is my solution code(C) for this problem. Doesn't handle some cases correctly, where there are powers of two numbers involved in between the two input numbers, trying to see if i can fix that:
int sparse_binary_count (const string &S,const string &T,int K)
{
char buf[50];
char *str1,*tptr,*Sstr,*Tstr;
int i,len1,len2,cnt=0;
long int num1,num2;
char *pend,*ch;
Sstr = (char *)S.c_str();
Tstr = (char *)T.c_str();
str1 = (char *)malloc(300001);
tptr = str1;
num1 = strtol(Sstr,&pend,2);
num2 = strtol(Tstr,&pend,2);
for(i=0;i<K;i++)
{
buf[i] = '0';
}
buf[i] = '\0';
for(i=num1;i<=num2;i++)
{
str1 = tptr;
if( (i & (i-1))==0)
{
if(i >= (pow((float)2,(float)K)))
{
cnt++;
continue;
}
}
str1 = myitoa(i,str1,2);
ch = strstr(str1,buf);
if(ch == NULL)
continue;
else
{
if((i % 2) != 0)
cnt++;
}
}
return cnt;
}
char* myitoa(int val, char *buf, int base){
int i = 299999;
int cnt=0;
for(; val && i ; --i, val /= base)
{
buf[i] = "0123456789abcdef"[val % base];
cnt++;
}
buf[i+cnt+1] = '\0';
return &buf[i+1];
}
There was an information within the test details, showing this specific case. According to this information, any power of 2 is considered K-sparse for any K.
You can solve this simply by binary operations on integers. You are even able to tell, that you will find no K-sparse integers bigger than some specific integer and lower than (or equal to) integer represented by T.
As far as I can see, you must pay also a lot of attention to the performance, as there are sometimes hundreds of milions of integers to be checked.
My own solution, written in Python, working very efficiently even on large ranges of integers and being successfully tested for many inputs, has failed. The results were not very descriptive, saying it does not work as required within question (although it meets all the requirements in my opinion).
/////////////////////////////////////
solutions with bitwise operators:
no of bits per int = 32 on 32 bit system,check for pattern (for K=2,
like 1001, 1000) in each shift and increment the count, repeat this
for all numbers in range.
///////////////////////////////////////////////////////
int KsparseNumbers(int a, int b, int s) {
int nbits = sizeof(int)*8;
int slen = 0;
int lslen = pow(2, s);
int scount = 0;
int i = 0;
for (; i < s; ++i) {
slen += pow(2, i);
}
printf("\n slen = %d\n", slen);
for(; a <= b; ++a) {
int num = a;
for(i = 0 ; i < nbits-2; ++i) {
if ( (num & slen) == 0 && (num & lslen) ) {
scount++;
printf("\n Scount = %d\n", scount);
break;
}
num >>=1;
}
}
return scount;
}
int main() {
printf("\n No of 2-sparse numbers between 5 and 15 = %d\n", KsparseNumbers(5, 15, 2));
}