I am trying to learn pointers which is a real PITA when you don't quite fully understand it.
I am trying to print all the elements in the array but only the first element is printed.
#include <stdio.h>
int count(const int* numbers, int size)
{
for(; numbers < size; numbers++)
{
printf("%d", *numbers);
}
}
int main(void)
{
int numbers[] = {3, 4, 6, 3, 46};
int result = count(numbers, 5);
printf("%d\n", result);
return 0;
}
The loop in the count function does not seem to work properly since it is only looping through one time but I can't understand why.
The comparison numbers < size is wrong.
You have 3 options:
Have a separate index variable:
int count;
for(count = 0; count < size; count++)
{
printf("%d", numbers[count]);
}
Have a separate "cursor" pointer:
const int * const end = numbers + size;
for(; numbers < end; numbers++)
{
printf("%d", *numbers);
}
Decrement size:
for(; size != 0; size--, numbers++)
{
printf("%d", *numbers);
}
the count() function should be
int count(const int* numbers, int size)
{
for(; size > 0; numbers++, size--)
{
printf("%d", *numbers);
}
}
Because numbers is a pointer, it contains an address. size is an int and equals 5. The address is not 5, nor is it even near 5.
You might save the start address and calculate the offset:
int count(const int* numbers, int size)
{
const int* start = numbers;
for(; (int)(numbers - start) < size; numbers++)
{
printf("%d\n", *numbers);
}
}
Related
So I want to split each digit of a decimal number into an array. I have the following code:
#include <stdio.h>
int * splitNumberIntoArr(int num) {
int i = num;
int modulus,newNum;
static int arr[5];
int j = 0;
while (i > 0) {
modulus = i % 10;
newNum = i / 10;
arr[j] = modulus;
j++;
i = newNum;
};
return arr;
};
int main() {
int num;
printf("Provide a number:\t");
scanf("%d", &num);
int *arr;
arr = splitNumberIntoArr(num);
int k;
for(k = 0; k <= sizeof(arr) / sizeof(arr[0]); k++) {
printf("%d\n",arr[k]);
return 0;
};
When num is an integer consising of 3 digits, the code works how it is supposed to.
However, when the input consists of more than 3 digits, the array that is returned by the splitNumberIntoArr()
function only returns an array of length 2.
for example,
Since I am new to C, I struggle to understand why this problem even exists, taking into consideration the fact that the declared array is of length 5: static int arr[5];
Your help would be greatly appreciated.
Try something like this:
#include <stdio.h>
#include <string.h> // for memset
void splitNumberIntoArr(int num, int *arr) {
int i = num;
int modulus, newNum;
int j = 0;
while (i > 0) {
modulus = i % 10;
newNum = i / 10;
arr[j] = modulus;
j++;
i = newNum;
};
}
int main() {
int num;
scanf("%d", &num);
int arr[32];
memset(arr, -1, sizeof(arr));
splitNumberIntoArr(num, arr);
for (int k = 0; k < sizeof(arr) / sizeof(arr[0]) && arr[k] != -1; k++) {
printf("%d\n",arr[k]);
}
}
In main(), the sizeof(arr) is known, because it lies on the stack.
I want to write a function, who gives me the maximum of an array and it should be with call by reference.
Here is my Code:
void max_array (int *array[], int len, int *max){
for (int i = 0; i < len; ++i) {
if (*max < &array[i]){
*max = array[i];
}
}
}
int main() {
void print_array (int array [], int len);
int array[] = {5,3,2,6,4,6,1};
int len = 8;
int max = 0;
max_array(array, len, &max);
printf("Max of Array: %d \n", max);
return 0;
}
Like u see there is something wrong.
My Output is like 158879987 so an address.
You are storing 8 in variable len, however your array has only 7 elements.
In the function, you have specified the first parameter incorrectly. Arrays are always passed by reference, you don't need a * and [], choose one.
void max_array (int *array, int len, int *max){
for (int i = 0; i < len; ++i) {
if (*max < array[i]){
*max = array[i];
}
}
}
remember to alter the value in the len variable.
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;
}
I'm trying to find the union of two sets of 10 digit numbers, I'm passing along three int arrays: first, second, and comp (this will hold the union set).
So far, I've added first and second into one array. I was thinking about finding the matching indices in comp[] then filter through deleting them. I figure there's a much easier way. Can anyone give me a hint?
Basically I'm taking
first[] = [1,2,3,4,5,6,7,8,9,10];
second[] = [1,2,3,4,11,12,13,14,15,16];
and I want to return
comp[] = [5,6,7,8,9,10,11,12,13,14,15,16];
The numbers won't necessarily be in order.
int compound(int first[],int second[],int comp[]){
int i=0;
int indicies[20];
for(int j = 0; j<SIZE; j++){
comp[i]=first[j];
i++;
}
for(int k = 0; k<SIZE; k++){
comp[i]=second[k];
i++;
}
int z=0;
for(int l = 0; l<SIZE*2; l++){
for(int m = 0; m<SIZE*2; m++){
if(comp[l]==comp[m]){
indicies[z]=m;
z++;
}}}
return 0;
}
A first good step is (nearly) always sorting.
Sort both input-sets (unless you know they are already sorted).
Then iterate over both at once (two indices) and only add those elements to the output which fulfill your criteria (seems to be union minus intersection, thus only in one).
Bonus: The output-set will be sorted.
I suggest you start by writing a contains(int[], int) method like
#include <stdio.h>
#include <stdbool.h>
bool contains(int arr[], int val) {
int offset;
for (offset = 0; arr[offset] != '\0'; offset++) {
if (arr[offset] == val) return true;
}
return false;
}
Then your compound method could be implemented using it with something like
int compound(int first[],int second[],int comp[]){
int i=0;
int j;
for(j = 0; first[j] != '\0'; j++){
int val = first[j];
if (contains(second, val) && !contains(comp, val))
comp[i++] = val;
}
return i;
}
Finally, you can test it like
int main(int argc, char *args[]) {
int a[] = {1,2,3,'\0'};
int b[] = {2,3,4,'\0'};
int c[3];
int count = compound(a,b,c);
int i;
for (i = 0; i < count; i++) {
printf("%i\n", c[i]);
}
}
Output is
2
3
If the numeric range is small you could do this:
#include <stdio.h>
#define MAX 20 // small numeric range
#define sz(a) (sizeof(a)/sizeof(*(a)))
int xunion(int *a, int sa, int *b, int sb, int *c) {
int n[MAX] = {0};
for (int i=0; i<sa; i++) n[a[i]] = 1;
for (int i=0; i<sb; i++) n[b[i]] = 1;
int j=0;
for (int i=0; i<MAX; i++) if (n[i]) c[j++] = i;
return j;
}
void prn(int *a, int s) {
while (s-- > 0) printf("%d ", *a++);
putchar('\n');
}
int main() {
int a[] = {6, 3, 4, 7, 5};
int b[] = {2, 4, 5, 7, 6, 3};
int c[MAX];
prn(a, sz(a));
prn(b, sz(b));
int n = xunion(a, sz(a), b, sz(b), c);
prn(c, n);
return 0;
}
I am trying to find the max number in an array. I have created a function and I am using the following code:
int maxValue( int myArray [], int size)
{
int i, maxValue;
maxValue=myArray[0];
//find the largest no
for (i=0;i)
{
if (myArray[i]>maxValue)
maxValue=myArray[i];
}
return maxValue;
}
However I get a syntax error before ) token. What am I doing wrong and am I even doing this right? Any help would be greatly appreciated.
You must pass a valid array with at least one member to this function:
#include<assert.h>
#include<stdio.h>
#include<stdlib.h>
#include<time.h>
int
maxValue(int myArray[], size_t size) {
/* enforce the contract */
assert(myArray && size);
size_t i;
int maxValue = myArray[0];
for (i = 1; i < size; ++i) {
if ( myArray[i] > maxValue ) {
maxValue = myArray[i];
}
}
return maxValue;
}
int
main(void) {
int i;
int x[] = {1, 2, 3, 4, 5};
int *y = malloc(10 * sizeof(*y));
srand(time(NULL));
for (i = 0; i < 10; ++i) {
y[i] = rand();
}
printf("Max of x is %d\n", maxValue(x, sizeof(x)/sizeof(x[0])));
printf("Max of y is %d\n", maxValue(y, 10));
return 0;
}
By definition, the size of an array cannot be negative. The appropriate variable for array sizes in C is size_t, use it.
Your for loop can start with the second element of the array, because you have already initialized maxValue with the first element.
A for loop has three parts:
for (initializer; should-continue; next-step)
A for loop is equivalent to:
initializer;
while (should-continue)
{
/* body of the for */
next-step;
}
So the correct code is:
for (i = 0; i < size; ++i)
the paren after the for seems to be missing some contents.
normally it should be something like
for (i=0; i<size; i++)
include:
void main()
{
int a[50], size, v, bigv;
printf("\nEnter %d elements in to the array: ");
for (v=0; v<10; v++)
scanf("%d", &a[v]);
bigv = a[0];
for (v=1; v<10; v++)
{
if(bigv < a[v])
bigv = a[v];
}
printf("\nBiggest: %d", bigv);
getch();
}