I updated my main and sequetialSearch and now it crashes when it runs. It compiles okay, but then crashes.
main.c
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <stdbool.h>
#include "percentage.h"
#include "sequentialSearch.h"
#define searchAmount 100
int main(int argc, char *argv[])
{
int numbers[100];
int searches[searchAmount];
int testAmounts[searchAmount];
int i;
int where;
int searchSuccess;
int searchUnsuccess;
int percent;
int looker;
int sum;
int average;
srand(time(NULL));
for (i = 0; i < 100; i++){
numbers[i] = rand() % 200;
}
for (i = 0; i < searchAmount; i++){
searches[i] = rand() % 200;
}
searchUnsuccess = 0;
searchSuccess = 0;
sum = 0;
for(i = 0; i < searchAmount; i++){
if(seqSearch(numbers, 100, searches[i], &where, &looker)){
searchSuccess++;
testAmounts[i] = looker;
}else{
searchUnsuccess++;
testAmounts[i] = looker;
}
}
for(i = 0; i < searchAmount; i++){
sum = sum + testAmounts[i];
}
average = sum / searchAmount;
percent = percentRate(searchSuccess, searchAmount);
printf("Total number of searches: %d\n", searchAmount);
printf("Total successful searches: %d\n", searchSuccess);
printf("Success Rate: %d%%\n", percent);
printf("Total number of tests ran: %d\n", average);
system("PAUSE");
return 0;
}
sequentialSearch.h
bool seqSearch (int list[], int last, int target, int* locn, int* looker){
*looker = 0;
while(*looker < last && target != list[*looker]){
*looker++;
}
*locn = *looker;
return(target == list[*looker]);
}
Pass looker in by reference, so that you can access its value from the caller.
int looker;
...
for(i = 0; i < searchAmount; i++){
if(seqSearch(numbers, 100, searches[i], &where, &looker)){
searches[i] += looker;
searchSuccess++;
}else{
searchUnsuccess++;
}
}
bool seqSearch (int list[], int last, int target, int* locn, int *looker){
*looker = 0;
while(*looker < last && target != list[*looker]){
(*looker)++;
}
*locn = *looker;
return(target == list[*looker]);
}
By the way, you may wish to reconsider defining functions in your header file; this could cause problems with duplicate symbol when linking if you have more than one c file including this file.
Why not just pass looker in as an int*, use it essentially as you have been, look at the value after seqSearch(...) returns, and add it to a running total back in main()?
One problem is that the increment of looker in seqSearch is incrementing the pointer rather than the value. It should probably be:
(*looker)++;
Related
The rest of my functions work fabulously, however the last function has my goat. The goal of this function is to use pointers to obtain the values of two different arrays and add those values to a third array. However, when I run the main method to make the function run, it pauses for a second and provides a wedge exit code that does not work.
I've tried removing the if((sizeof(*ptr1)) == (sizeof(*ptr2)){
---insert code here---
}
from the for loop, however, the problem seems to be just the for loop itself.
//===================================Broken Code========================================
#include <stdio.h>
#define MAXIMUM 1000
int sumArrays(int arr1[], int arr2[]);
int addArrays(int arr1[], int arr2[]);
int main()
{
int arrayOne[MAXIMUM];
int arrayTwo[MAXIMUM];
for(int i = 0; i <= MAXIMUM; i++)
arrayOne[i] = i;
printf("Arrayone %d\n", arrayOne);
for(int j = 0; j <= MAXIMUM; j++)
arrayTwo[j] = j;
printf("ArrayTwo %d\n", arrayTwo);
printf(" The sum of the arrays is : %d\n",sumArrays(arrayOne, arrayTwo));
printf("%d", addArrays(arrayOne, arrayTwo));
return 0;
}
int sumArrays(int arr1[],int arr2[]){
int *ptr_1;
int *ptr_2;
ptr_1 = &arr1[0];
ptr_2 = &arr2[0];
int sum;
for(int i = 0; i < MAXIMUM; i++){
sum += *ptr_1 + i;
sum += *ptr_2 + i;
}
return sum;
}
int addArrays(int arr1[],int arr2[]){
int *ptr1 = &arr1[0];
int *ptr2 = &arr2[0];
int sum = 0;
int i = 0;
int arr3[0];
if(sizeof(*ptr1) == sizeof(*ptr2)){
for(int i = 0; i < MAXIMUM; i++){
sum += *ptr1 +i;
sum += *ptr2 +i;
arr3[i] = sum;
}
}
printf("The value of array3 is %d", arr3);
}
The other function works perfectly, but the addArrays function does a wedge exit and doesn't cooperate.
I expect the addArrays function to take the elements from each array, add them together and assign them to the third array.
Thank you for your time.
UPDATE: WORKING CODE
#include <stdio.h>
#define MAXIMUM 1000
#define ARRAY_SZ(x) (sizeof(x) / sizeof((x)[0]))
int sumArrays(int arr1[], int arr2[], size_t len);
int addArrays(int arr1[], int arr2[], int arr3[], size_t len);
int main()
{
int arrayOne[MAXIMUM];
int arrayTwo[MAXIMUM];
int arrayThree[MAXIMUM];
for(int i = 0; i <= MAXIMUM; i++)
arrayOne[i] = i;
printf("Array One %d\n", ARRAY_SZ(arrayOne));
for(int j = 0; j <= MAXIMUM; j++)
arrayTwo[j] = j;
printf("Array Two %d\n", ARRAY_SZ(arrayTwo));
printf(" The sum of the arrays is : %d\n",sumArrays(arrayOne, arrayTwo, ARRAY_SZ(arrayOne)));
printf("%d", addArrays(arrayOne, arrayTwo, arrayThree, MAXIMUM));
return 0;
}
int sumArrays(int arr1[],int arr2[], size_t len){
int *ptr_1;
int *ptr_2;
ptr_1 = &arr1[0];
ptr_2 = &arr2[0];
int sum = 0 ;
for(int i = 0; i < len; i++){
sum += *ptr_1++;
sum += *ptr_2++;
}
return sum;
}
int addArrays(int arr1[],int arr2[], int result[], size_t len){
int *ptr1 = &arr1[0];
int *ptr2 = &arr2[0];
int *ptr3 = &result[0];
int sum = 0;
int sum2 = 0;
int i = 0;
for(int i = 0; i < MAXIMUM; i++){
sum = *ptr1 ++;
sum += *ptr2 ++;
result[i] = sum;
printf("The result of array 3 is %d\n", *ptr3++);
}
}
Here are some notes:
When you assign/pass/print the and array using the name of the array, you are actually passing the memory location of the first element in the array (a pointer).So when you write:
printf("Arrayone %d\n", arrayOne);
You will see the memory address of the first element of the array being printed. If you would like to print the entire array you will need to loop through it. In this case you would be printing 1000 integers which might be undesirable.
void printArray(int * array, size_t len)
{
while(len--)
{
printf("%d ", *array++);
}
}
To get the number of elements in an array you can do something like this:
sizeof(arrayOne) / sizeof(arrayOne[0])
and you can put it in a macro like this:
#define ARRAY_SZ(x) (sizeof(x) / sizeof((x)[0]))
and call it like this:
ARRAY_SZ(arrayOne);
You cannot get the array size if you are receiving an array in a function (it has decayed to a pointer), instead you should pass the array size to the function too. Here because you initialize the arrays with the size MAXIMUM we don't actually need to calculate the array size, but we can just to show it works.
If you want to return an array (like in addArrays()) you should create an empty array and pass it to the function, then the function can update the array with the result.
When looping through an array you never want to do array[maximum] because the array indices range from 0 to maximum - 1
#include <stdio.h>
#define MAXIMUM 1000
#define ARRAY_SZ(x) (sizeof(x) / sizeof((x)[0]))
int sumArrays(int arr1[], int arr2[]);
int addArrays(int arr1[], int arr2[]);
int main()
{
int arrayOne[MAXIMUM];
int arrayTwo[MAXIMUM];
int arrayThree[MAXIMUM];
for(int i = 0; i < MAXIMUM; i++)
arrayOne[i] = i;
printf("Array one size %d\n", ARRAY_SZ(arrayOne));
for(int j = 0; j < MAXIMUM; j++)
arrayTwo[j] = j;
printf("Array Two size %d\n", ARRAY_SZ(arrayTwo));
printf(" The sum of the arrays is : %d\n",sumArrays(arrayOne, arrayTwo, ARRAY_SZ(arrayOne)));
addArrays(arrayOne, arrayTwo, arrayThree, MAXIMUM);
return 0;
}
int sumArrays(int arr1[],int arr2[], size_t len)
{
int *ptr_1;
int *ptr_2;
ptr_1 = &arr1[0];
ptr_2 = &arr2[0];
int sum;
for(int i = 0; i < len; i++){
sum += *ptr_1 + i;
sum += *ptr_2 + i;
}
return sum;
}
void addArrays(int arr1[], int arr2[], int result[], size_t len){
int *ptr1 = arr1;
int *ptr2 = arr2;
int sum = 0;
int i = 0;
for(int i = 0; i < len; i++){
sum = *ptr1 +i;
sum += *ptr2 +i;
result[i] = sum;
}
}
can you help me with code which returns partial sum of 'X' numbers in array in c?
Complete :
int arr_sum( int arr[], int n )//Recursive sum of array
{
if (n < 0) //base case:
{
return arr[0];
}
else
{
return arr[n] + arr_sum(arr, n-1);
}
}
void sum_till_last (int *ar,int si )
{
**int sum,i;// the problem some where here
ar=(int*) malloc(si*sizeof(int));
for (i=0; i<si;i++)
{
sum=arr_sum(ar,i);
ar [i]=sum;
}
free (ar);**
}
void main ()
{
int i;
int a [5];
for (i = 0; i < 5; i++)
scanf_s("%d", &a[i]);
sum_till_last(a,5);
printf("%d\n",a[5]);
}
\i want to create new array with this this legality:
My input :
4
13
23
21
11
The output should be (without brackets or commas):
4
17
40
61
72
Now when we can see the full code, it's quite obvious that the problem is in the sum_till_last function where you overwrite the pointer you pass to the function with some new and uninitialized memory you allocate.
Drop the allocation (and the call to free of course). And fix the logical bug in arr_sum that causes you to get arr[0] + arr[0] when i is zero.
Here you go:
#include <stdio.h>
int main () {
int in_arr[5] = {4,13,23,21,11};
int out_arr[5];
int p_sum =0;
int i;
for ( i=0;i<5;i++){
out_arr[i] = in_arr[i]+p_sum;
p_sum=p_sum+in_arr[i];
}
for (i=0;i<5;i++){
printf("%d", out_arr[i] );
}
}
Fix according to your policy
#include <stdio.h>
#include <stdlib.h>
int arr_sum(int arr[], int n){
if (n == 0){//Change to this
return arr[0];
} else {
return arr[n] + arr_sum(arr, n-1);
}
}
void sum_till_last(int *ar, int si){
int sum,i;
int *temp = malloc(si * sizeof(int));//variable name ar is shadowing parameter name ar.
for(i = 0; i < si; i++){
temp[i] = arr_sum(ar, i);
if(i)
putchar(' ');
printf("%d", temp[i]);//need print out :D
}
free(temp);
}
int main(void){
int i, a[5];
for (i = 0; i < 5; i++)
scanf_s("%d", &a[i]);
sum_till_last(a, 5);
//printf("%d\n",a[5]);<-- this print only one element. and It's out of bounds element XD
}
I just made it simple so it´s easy to understand :)
I´m assuming "n" is always equal or less then array element number. Then you just print the SUM.
#include <stdio.h>
int arr_sum( int arr[], int n ){
int i=0,SUM=0;
for(; i < n;i++){
SUM= SUM+ arr[i];
printf("%d ",SUM);
}
}
int main(void) {
int array[] = {4, 13, 23, 21, 11};
arr_sum(array,5);
return 0;
}
Earlier I posted a question about the coin vending machine problem (the minimum number of coins required). Turns out the issue was a typo in a for loop, so now the program works. The original question was this:
As the programmer of a vending machine controller your are required to compute the minimum number of coins that make up the required change to give back to customers. An efficient solution to this problem takes a dynamic programming approach, starting off computing the number of coins required for a 1 cent change, then for 2 cents, then for 3 cents, until reaching the required change and each time making use of the prior computed number of coins. Write a program containing the function ComputeChange(), that takes a list of valid coins and the required change. This program should repeatedly ask for the required change from the console and call ComputeChange() accordingly. It should also make use of “caching”, where any previously computed intermediate values are retained for subsequent look-up.
The issue is that the code makes use of recursion, so it takes quite a long time to evaluate large values. Making use of caching should improve the issue, but I have no idea how to go about it. The code can be found below.
#include <stdio.h>
#include <limits.h>
int computeChange(int[],int,int);
int min(int[],int);
int main(){
int cur[]={1,2,5,10,20,50,100,200};
int n = sizeof(cur)/sizeof(int);
int v;
printf("Enter a value in euro cents: ");
scanf("%d", &v);
printf("The minimum number of euro coins required is %d", computeChange(cur, v, n));
return 0;
}
int computeChange(int cur[], int v, int n){
if(v < 0)
return INT_MAX;
else if(v == 0)
return 0;
else{
int possible_mins[n], i;
for(i = 0; i < n; i++){
possible_mins[i]=computeChange(cur, v-cur[i], n);
}
return 1+min(possible_mins, n);
};
}
int min(int a[], int n){
int min = INT_MAX, i;
for(i = 0; i < n; i++){
if((a[i]>=0) && (a[i]< min))
min = a[i];
}
return min;
}
With your existing code:
#include <stdio.h>
#include <limits.h>
int computeChange(int[],int,int);
int min(int[],int);
void initChange ();
int change [MAX]; //used for memoization
int main(){
int cur[]={1,2,5,10,20,50,100,200};
int n = sizeof(cur)/sizeof(int);
int v;
initChange ();
printf("Enter a value in euro cents: ");
scanf("%d", &v);
printf("The minimum number of euro coins required is %d", computeChange(cur, v, n));
return 0;
}
void initChange () {
int i =0;
for (i = 0; i < MAX; i++) {
change[i] = INT_MAX;
}
}
int computeChange(int cur[], int v, int n){
if(v < 0)
return INT_MAX;
else if(v == 0)
return 0;
else{
if (change[v] == INT_MAX) {
int possible_mins[n], i;
for(i = 0; i < n; i++){
possible_mins[i]=computeChange(cur, v-cur[i], n);
}
change[v] = 1 + min(possible_mins, n); // memoization
}
return change[v];//you return the memoized value
};
}
int min(int a[], int n){
int min = INT_MAX, i;
for(i = 0; i < n; i++){
if((a[i]>=0) && (a[i]< min))
min = a[i];
}
return min;
}
I already posted a solution using loops in your previous question. I will post it again here:
So the below is the code snippet for your problem using memoization and dynamic programming. The complexity is O(Val*numTypesofCoins).
In the end, change[val] will give you the min number of coins for val.
int main (void) {
int change [MAX];
int cur[]={1,2,5,10,20,50,100,200};
int n = sizeof(a)/sizeof(int);
int val; //whatever user enters to get the num of coins required.
printf("Enter a value in euro cents: ");
scanf("%d", &val);
for (i=0; i <= val; i++) {
change[i] = INT_MAX;
}
for (i=0; i < n; i++) { // change for the currency coins should be 1.
change[cur[i]] = 1;
}
for (i=1; i <= val; i++) {
int min = INT_MAX;
int coins = 0;
if (change[i] != INT_MAX) { // Already got in 2nd loop
continue;
}
for (j=0; j < n; j++) {
if (cur[j] > i) { // coin value greater than i, so break.
break;
}
coins = 1 + change[i - cur[j]];
if (coins < min) {
min = coins;
}
}
change[i] = min;
}
}
I was trying to write a program that calculates prime numbers using threads and the program was working but not giving the desired results (it was telling all numbers were prime numbers). Today I tried to run the program again and I'm getting a segmentation fault even though I didn't alter my program. I tried using gdb to find when it was happening and I think it's happening on the pthread_join function.
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
int n_threads; // number of threads
int* numbers; // array of numbers
int elements_per_thread;
int isPrime(int n){
int i = 0;
for(i=0; i < n; i++)
if(n%i == 0)
return 0;
return 1;
}
void * threadPrime(void * arg){
int* idxp = (int*)arg;
int idx = *idxp;
int start = idx* elements_per_thread;
int finish = (idx+1)*elements_per_thread-1;
int i;
for(i=start; i<finish; i++)
if(!isPrime(i))
numbers[i]=0;
pthread_exit(NULL);
}
int main(int argc, char* argv[]) {
if (argc != 3) {
printf("usage: %s largest_number number_threads\n", argv[0]);
return 1;
}
int largest_number = atoi(argv[1]); // value of the largest number to test for primality
int n_numbers = largest_number-1; // number of numbers to test
n_threads = atoi(argv[2]);
// create and fill vector of numbers to test
numbers = (int *)malloc(n_numbers*sizeof(int)) ; // allocate a vector for n_numbers integers
int i;
for (i = 2; i <= largest_number; i++)
numbers[i-2] = i;
int* id = (int *)malloc(n_threads*sizeof(int));
// compute primes
pthread_t* thid = (pthread_t *)malloc(n_threads*sizeof(int));
for(i=0;i<n_threads;i++){
id[i] = i;
if(pthread_create(&thid[i],NULL,threadPrime,(void*)(id+i)) != 0){
printf("Erro\n");
exit(0);
}
}
for(i=0;i<n_threads;i++){
if(pthread_join(thid[i],NULL) != 0){
printf("Erro\n");
exit(0);
}
}
// print result
printf("Primes:");
int n_primes = 0;
for (i = 0; i < n_numbers; i++)
if (numbers[i]) {
n_primes++;
printf (" %d", numbers[i]);
}
printf("\nTotal: %d primes\n", n_primes);
return 0;
}
Problem solved. Correct code below.
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
int n_threads; // number of threads
int* numbers; // array of numbers
int elements_per_thread;
int isPrime(int n){
int i = 0;
for(i=2; i < n; i++)
if(n%i == 0)
return 0;
return 1;
}
void * threadPrime(void * arg){
int* idxp = (int*) arg;
int idx = *idxp;
int start = idx*elements_per_thread;
int finish = (idx+1)*elements_per_thread;
int i;
for(i=start; i<=finish; i++)
if(!isPrime(numbers[i]))
numbers[i]=0;
pthread_exit(NULL);
}
int main(int argc, char* argv[]) {
if (argc != 3) {
printf("usage: %s largest_number number_threads\n", argv[0]);
return 1;
}
int largest_number = atoi(argv[1]); // value of the largest number to test for primality
int n_numbers = largest_number-1; // number of numbers to test
n_threads = atoi(argv[2]);
// create and fill vector of numbers to test
numbers = (int *)malloc(n_numbers*sizeof(int)) ; // allocate a vector for n_numbers integers
int i;
for (i = 2; i <= largest_number; i++)
numbers[i-2] = i;
int* id;
id = (int *)malloc(n_threads*sizeof(int));
// compute primeselements_per_thread = n_numbers/n_threads;
elements_per_thread = (n_numbers/n_threads)+1;
pthread_t* thid = malloc(n_threads*sizeof(*thid));
for(i=0;i<n_threads;i++){
id[i] = i;
if(pthread_create(&thid[i],NULL,threadPrime,(void*)(id+i)) != 0){
printf("Erro\n");
exit(0);
}
}
for(i=0;i<n_threads;i++){
if(pthread_join(thid[i],NULL) != 0){
printf("Erro\n");
exit(0);
}
}
// print result
printf("Primes:");
int n_primes = 0;
for (i = 0; i < n_numbers; i++)
if (numbers[i]) {
n_primes++;
printf (" %d", numbers[i]);
}
printf("\nTotal: %d primes\n", n_primes);
return 0;
}
There are a number of issues:
1) The starting index for the loop should be 2. Otherwise, you are going to have divide by zero error here:
for(i=0; i < n; i++) // should be i=2
if(n%i == 0)
return 0;
2) elements_per_thread is not set at all. So it's going to be 0 (since it's a global variable) and the loops in thread function will never be called. Set it in main():
elements_per_thread = n_numbers/n_threads;
3) When you call isPrime() you are passing i. But you really wanted to pass numbers[i]. You also want to include the finish in the primality test. So it should be
for(i=start; i<=finish; i++)
if(!isPrime(numbers[i]))
numbers[i]=0;
4) The allocation for thread array is wrong. It should be
pthread_t* thid = malloc(n_threads * sizeof *thid);
There are more efficient ways to test primes (e.g. you only need to check upto n/2 to see if it's prime). But once you fix the above issues, you'll have a working code and think about improving it later.
You didn't allocate the right amount of memory for thid. This is the main reason for your segmentation fault.
pthread_t* thid = (pthread_t *)malloc(n_threads*sizeof(int));
should be
pthread_t* thid = malloc(n_threads*sizeof(p_thread));
(you don't need to cast malloc in C)
This is why I don't usually use an explicit type as the operand of sizeof, and instead just use the variable name so that the compiler can deduce the type itself.
pthread_t* thid = malloc(n_threads*sizeof(*thid));
I am attempting to pass an array as an argument to a function in a new thread using pthread_create, is this possible? I have an array of integers and a calculate average method that is called from the create thread method but I cannot seem to pass my array into the method correctly. Here is my code:
int nums[];
int average;
int size = 0;
void *calcAvg(int *nums[]);
int main(int argc, char *argv[]){
/* initialize an array of the integers to be passed */
nums[argc - 1];
for(int i = 0; i < argc - 1; i++){
nums[i] = atoi(argv[i + 1]);
size++;
}
/* Thread Identifier */
pthread_t avgThread;
pthread_create(&avgThread, NULL, calcAvg, nums);
pthread_join(avgThread, NULL);
printf("average= %d", average);
}
void *calcAvg(int *nums[]){
int sum;
for(int i = 0; i < size; i++){
sum += nums[i];
}
average = sum / (size);
pthread_exit(0);
}
there is lots of problem in your code, i fix some to compile
hope it will help
compile: gcc -o main main.c -lpthread
execute: ./main 2 5
output: 3
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
int average;
int size = 0;
void *calcAvg(void *arg);
int main(int argc, char *argv[]){
/* initialize an array of the integers to be passed */
int *nums = (int*)malloc((argc - 1)*sizeof(int));
int i = 1;
for(i = 1; i < argc ; i++){
nums[i-1] = atoi(argv[i]);
size++;
}
/* Thread Identifier */
pthread_t avgThread;
pthread_create(&avgThread, NULL, calcAvg, (void*)nums);
pthread_join(avgThread, NULL);
printf("average = %d \n",average);
free(nums);
}
void *calcAvg(void *arg){
int *val_p = (int *) arg;
int sum = 0;
int i = 0;
for( i = 0; i < size; i++){
sum += val_p[i];
}
average = sum / (size);
pthread_exit(0);
}
Change the following
void *calcAvg(int *nums[]){
int sum;
for(int i = 0; i < size; i++){
sum += nums[i];
}
average = sum / (size);
pthread_exit(0);
}
to
void *calcAvg(void *arg){
int *val_p = (int *) arg;
int sum;
for(int i = 0; i < size; i++){
sum += val_p[i];
}
average = sum / (size);
pthread_exit(0);
}
The main issue that 'pthread_create()' takes a void pointer as its last argument. You are trying to pass to it an array of pointers to integers. Issue "man pthread_create" at the terminal to see the argument types you should be passing.
What you really want to do is just pass the of array integers to the thread. In C, array indexing is just notation for pointer arithmetic. Writing nums[i] is equivalint to &nums[0] + i or just nums+i. The last case works because the name of an array in C can be used as a pointer to the first element of the array.
change void *calcAvg(int *nums[]) to void *calcAvg(void* thread_args). Then in 'calcAvg' write int *nums = (int*)thread_args. Now you can use nums in that function just as if you had called calcAvg(nums), which in in essence you have done.