I have a 2d array which has same numbers in a row.
I have to find the index of the elements in increasing order and put it in another array.
For example, assume that the input array has the following numbers:
int test[5][2]= { {12,12},{3,3},{14,14},{5,5},{8,8} }.
I have to output in result array with:
result[5] = {1,3,4,0,2}.
Just the index of the elements in increasing order...
I wrote this program, but the result array is always 1.
int main()
{
int N=5;
int result[5];
int test[5][2] = { {12,12},{3,3},{14,14},{5,5},{8,8} };
int i,j;
int smallindex = 0;
for (j=0; j<5; j++)
{
for (i=1; i<5; i++)
{
if (test[i][0] < test[i-1][0])
{
smallindex=i;
}
}
result[j]=smallindex;
}
for (j=0; j<5; j++)
{
printf("%d \t ", result[j]);
}
}
Can anyone tell me what is wrong in this?.
thanks
Make little modification for if statement in your code.
for(i=0;i<5;i++)
{
smallindex=0;
for(j=0;j<5;j++) {
//try to avoid comparing same element by checking i==j
if(test[i][0]<test[j][0])
smallindex++; // check each element with all elements.count how many elements are greater than specific element.increment count and at the end of inner loop assign to result array.
}
result[i]=smallindex;
}
Related
void interclas(int *ptr,int *vec, int *c, int n) {
int i,j,tmp;
tmp=0;
for (i=0;i++;i<n)
for (j=0;i++;j<n)
{
if (vec[j]<=ptr[i])
c[tmp]=vec[j];
else
c[tmp]=ptr[i];
tmp++;
}
}
int main() {
int i,n;
int *ptr,*vec,*c;
printf("Nr. of elements of initial arrays : 5 \n");
n=5;
vec=(int*)malloc( n * sizeof(int));
ptr=(int*)malloc( n * sizeof(int));
c=(int*)malloc( 2 * n * sizeof(int));
for (i=0;i<n;i++) {
scanf("%d",&ptr[i]);
}
for (i=0;i<n;i++) {
scanf("%d",&vec[i]);
}
printf("\n");
printf("Initial arrays are : ");
for (i=0;i<n;i++) {
printf("%d ",ptr[i]);
}
printf("\n");
for (i=0;i<n;i++) {
printf("%d ",vec[i]);
}
interclas(ptr,vec,&c,n);
printf("Merged array is : ");
for (i=0;i<10;i++) {
printf("%d ",c[i]);
}
return 0;
}
So I'm trying to merge two sorted arrays into one new one using pointers with the function 'interclas'. I tried using the same method to sort an array with a pointer in a function and it worked just fine. Now as you can see, it stores the adress of the variable rather than the variable itself.
If I run this, it stores the adresses of the arrays. How can I fix this? (I'm still new to pointers)
In your method's body, change:
for (i=0;i++;i<n)
for (j=0;i++;j<n)
to this:
for (i=0; i<n; i++)
for (j=0; j<n; j++)
and then change the call to your method, from this:
interclas(ptr, vec, &c, n);
to this:
interclas(ptr, vec, c, n);
since the prototype expects a pointer to an int, for the third parameter.
The logic of your method is also flawed, try to put some printfs (e.g. printf("here i = %d, j = %d, ptr[i] = %d, vec[j] = %d, tmp = %d\n", i, j, ptr[i], vec[j], tmp);) to see what values your variables have at its iteration - you only get the first two elements of the first array to be merged!
If you think about it, what you'd like to do is to go through the first element of array ptr and vec, and store the minimum of this two. If now that min was of array ptr, you'd like the next element of ptr to be taken into account, otherwise the next element of vec.
Take a pencil and a paper and sketch that algorithm - you'll see that it goes out nicely, but some leftover elements might be left behind, and not get inserted in the output array.
Driven from that observation, after traversing both the arrays and comparing elements, we will loop over the first array, if needed, to collect elements that were not visited. Similarly for the second array.
Coding that thought gives something like this:
void interclas(int *ptr,int *vec, int *c, int n) {
int i = 0, j = 0, tmp = 0;
// Traverse both arrays simultaneously,
// and choose the min of the two current elements.
// Increase the counter of the array who had
// the min current element.
// Increase the counter for the output array in
// any case.
while(i < n && j < n)
{
if(ptr[i] < vec[j])
{
c[tmp++] = ptr[i++];
}
else
{
c[tmp++] = vec[j++];
}
}
// Store remaining elements of first array
while (i < n)
c[tmp++] = ptr[i++];
// Store remaining elements of second array
while (j < n)
c[tmp++] = vec[j++];
}
Not the source of your problem, but Do I cast the result of malloc? No.
I have a homework problem that asks for my code to read a 10-length vector, order it in ascendant order and then print it. I'm trying to do this using a variable int k as a countable index, where the code verifies whether a particular position in the vector is greater than the other positions, and adds 1 to k for each smaller variable. Then, I create a second vector, and atrribute for its kth position this value of the first vector.
The compilation isn't pointing out any mistakes. The code runs, I inform the 10 values of the vector, then it returns a big number and crashes.
Could anyone help me? Thanks in advance.
#include <stdio.h>
#include <stdlib.h>
#include <locale.h>
int main ()
{
setlocale(LC_ALL, "Portuguese");
//creates two double vectors
double v[10], w[10];
//creates a int variable to be a countable index
int k = 0;
//asks for the user to inform the values of the vector
for (int i=0; i<=9; i++)
{
printf("Digite um número:\n");
scanf("%lf", &v[i]);
}
//Here, I create this loop to verify whether each position of the vector v is greater than the other positions.
for (int j=9; j>=0; j--)
{
//For the case j=9, I verify if it is greater than all the predecessor values, and add 1 to k for each case
if (j==9)
{
for (int t=j-1; t>=0; t--)
{
if (v[j]>v[t])
{
k+=1;
}
}
//I attribute this value of v to the kth position of the new vector, and restart the countable index
w[k]=v[j];
k=0;
continue;
}
//I do the same for the case in which j=0, verifying whether it is greater than the subsequent values
else if (j==0)
{
for (int s=j+1; s<=9; s++)
{
if (v[j]>v[s])
{
k+=1;
}
}
w[k]=v[j];
k=0;
continue;
}
//For all the other values of the vector, I test both whether they are greater than the
//predecessors and the subsequent values, and add 1 to k for each case
else
{
for (int t=j-1; t>=0; t--)
{
if (v[j]>v[t])
{
k+=1;
}
}
for (int s=j+1; s<=9; s--)
{
if (v[j]>v[s])
{
k+=1;
}
}
//I attribute this value to the kth position of the new vector and restart the countable index
w[k]=v[j];
k=0;
}
//Here my loop ends
}
//I print the new vector
for (int p=0; p<=9; p++)
{
printf(" %lf ",w[p]);
}
system("pause");
return 0;
}
for (int s=j+1; s<=9; s--) should have s++. I don't see anything else wrong but I'll check with gdb if that doesn't fix it.
I am currently working on a simple code to store and display top-right triangular matrix. Well, everything was fine till I tried to input 4x4 matrix structure and gave the input. The first array of structure's (called a) last value changed although I did not put any code to change ANY of the values in a. It happens in the mReorder() function. Then I tried some try-and-errors find out the problem in the 3rd row of mReorder() function. I wonder why and how to solve it.
Here is my complete code:
#include<stdio.h>
//CMO fashion
typedef struct
{
int row;
int col;
int val;
}term;
#define MAX_TERMS 10
term a[MAX_TERMS], b[MAX_TERMS];
void mReorder(void);
int main()
{
int n, i, j;
printf("Enter the number of rows: ");
scanf("%d", &n);
if (n<1 || n>MAX_TERMS)
{
printf("\nInvalid number of rows!!");
exit(0);
}
i=nCount(n);
mRead(n,i);
for (j=0; j<i+1; j++) printf("\n%d\t%d\t%d", a[j].col, a[j].row, a[j].val);
mReorder();
for (j=0; j<i+1; j++) printf("\n%d\t%d\t%d", a[j].col, a[j].row, a[j].val);
printf("\n");
for (j=0; j<i+1; j++) printf("\n%d\t%d\t%d", b[j].col, b[j].row, b[j].val);
mDisplay();
return 0;
}
void mReorder(void)
{
int i, j, k, m=1;
b[0].col=a[0].col;
b[0].row=a[0].row;
b[0].val=a[0].val;
for(i=0; i<a[0].col; i++)
for (j=1; j<=a[0].val; j++)
if (a[j].row==i)
{
b[m].col=a[j].col;
b[m].row=a[j].row;
b[m].val=a[j].val;
m++;
}
}
void mDisplay(void)
{
int i, j, k, m=1;
printf("\nThe resulting matrix is:\n");
for (i=0; i<b[0].col; i++)
{
//printf("\na");
for (k=0; k<i; k++) printf("%5c", '-');
for (j=i; j<b[0].col; j++)
{
printf("%5d", b[m].val);
m++;
}
printf("\n");
}
}
void mRead(int n, int x)
{
int i, j, m=1, val;
printf("\nEnter %d elements of the matrix: \n", x);
a[0].row=a[0].col=n;
a[0].val=x;
for (i=0; i<n; i++)
{
for (j=0; j<=i; j++)
{
scanf("%d", &val);
a[m].row=j;
a[m].col=i;
a[m].val=val;
m++;
}
}
}
int nCount(int n)
{
if (n==1)
return 1;
return (n+nCount(n-1));
}
Can you explain what's going on here?
You allocate enough space for 10 term items, but nCount(4) returns 10, and nCount(5) returns 15, etc. If you specify a value bigger than 4, you overflow your array boundaries, leading to undefined behaviour — which is something to be avoided at all costs. In practice, one of your two arrays tramples over the other, but what happens when you access the other array out of bounds is entirely up to the compiler. It may appear to work; it may crash horribly; it may corrupt other data structures.
Nominally, since you allocate 10 elements in the arrays a and b, you should be OK with the 4x4 data, but in mRead(), you set m = 1 to start with, so you end up writing to a[10] in the last iteration of the loop, which is outside the bounds of the array. Remember, C arrays are indexed from 0, so an array defined as SomeType array[N]; has elements from array[0] to array[N-1].
Note that you can rewrite nCount() as a simple (non-recursive) function:
static inline int nCount(int n) { return (n + 1) * n / 2; }
(which would need to appear before it is called, of course). Or, if you're stuck using an archaic compiler that doesn't support C99 or C11, drop the inline keyword.
I am trying to create this program that takes an int number from the user then randomizes a pair of numbers, based on the input, inside the an array of struct. Then it sorts this array based on the sum of the number pair the program randomized.
However my program won´t sort the array of struct. It doesn´t do the sorting properly and Im not sure why. Here is the code.
#define MAX 10
struct NumPair{
int n,m;
};
int main()
{
int i, j, amount=0;
NumPair NumPair[MAX];
srand(time(NULL));
printf("How many pair of numbers? (max 10): ");
scanf("%d", &amount);
for (i=0; i<amount; i++)
{
NumPair[i].n = rand() % 11;
NumPair[i].m = rand() % 11;
}
for (i=0; i<amount; i++)
{
for(j=1; j<amount; j++)
{
if( (NumPair[i].n+NumPair[i].m) > (NumPair[j].n+NumPair[j].m) )
{
int tmp;
tmp = NumPair[i].n;
NumPair[i].n = NumPair[j].n;
NumPair[j].n = tmp;
tmp = NumPair[i].m;
NumPair[i].m = NumPair[j].m;
NumPair[j].m = tmp;
}
}
}
for (i=0; i<amount; i++)
{
printf(" NumPair %d: (%d,%d)\n", i+1, NumPair[i].n, NumPair[i].m);
}
return 0;
}
What am I missing? It's probably something very silly.
Thanks in advance.
Your algorithm is incorrect. This little snippet:
for (i=0; i<amount; i++) {
for(j=1; j<amount; j++) {
will result in situations where i is greater than j and then you comparison/swap operation is faulty (it swaps if the i element is greater than the j one which, if i > j, is the wrong comparison).
I should mention that (unless this is homework or some other education) C has a perfectly adequate qsort() function that will do the heavy lifting for you. You'd be well advised to learn that.
If it is homework/education, I think I've given you enough to nut it out. You should find the particular algorithm you're trying to implement and revisit your code for it.
You are comparing iterators i with j. Bubble sort should compare jth iterator with the next one
for (i=0; i<amount; i++) //pseudo code
{
for(j=0; j<amount-1; j++)
{
if( NumPair[j] > NumPair[j+1] ) //compare your elements
{
//swap
}
}
}
Note that the second loop will go only until amount-1 since you don't want to step out of bounds of the array.
change to
for (i=0; i<amount-1; i++){
for(j=i+1; j<amount; j++){
I can't find any errors here. The purpose of the program is to thing all possible combinations of array elements and their sums. I'm trying to write a program which will return me an array of elements where every next one does not equal any previous one or the sum of any previous combinations of elements. I started like this and encountered an error: it says that program has stopped working...
#include <stdio.h>
int m[20];
void initm(int x[]) {
for(int i=0; i<20; i++) {
m[i]=i;
}
}
void sorter(int x[]) {
for(int i=0; i<20; i++) {
for(int j=0; j<20; j++) {
/* nested for loop to get all possible combinations */
printf("%d===%d===%d", x[i], x[j], x[i]+x[j]);
}
}
}
int main() {
initm(m[20]);
sorter(m[20]);
return 0;
}
m[20] reads an int one element beyond the end of your array so
initm(m[20]);
sorter(m[20]);
should be
initm(m);
sorter(m);