I have 2 simple functions, one function inputs in the the NxM array not including N+2 and M+2. So the original array must be surrounded by zeros and the other outputs the whole array. When the out function is called I have a very strange output:
But when I move the code to the main function everything is totally fine. I tried compiling this code in CodeBlocks and NetBeans.Behaviour is the same.
I don't know what's going on there. Can somebody explain?
.....
int main()
{
int array[N+2][M+2]={{0}};
local_in(N,M,array);
local_out(N,M,array);
return 0;
}
void local_in(int len, int len2,int arr[][len2])
{
int i;
int j;
for(i = 1; i <= len; i++)
for(j = 1; j <= len2; j++){
scanf("%d",&arr[i][j]);
}
}
void local_out(int len, int len2,int arr[][len2])
{
int i;
int j;
for(i = 0; i < len+2; i++){
for(j = 0; j < len2+2; j++)
printf("%d ",arr[i][j]);
printf("\n");
}
}
Your local_* functions pass the array as int arr[][len2]; but should use int arr[][len2+2] instead.
In general, the code should be much clearer if you passed the correct array dimensions around then implemented any policy on which items to read or write inside the local_* functions.
Related
I am working on an old exam and the problems states that a given array (int zahlen[]={1,4,5,1,5,7,9,2,3,4}) has values that are the same. The task is to replace the values that are the same with '-1'. After each replacement, a given variable, count, has to be increased by one.
My problem is that the variable count is two-times higher than normal (In this case there are only 3 of the same numbers and the variable shows 6.)
The function is called array_unique. I am would be grateful for a brief explanation of my mistake.
Here is my code:
#include <stdio.h>
#include <stdlib.h>
int main()
{
system("chcp 1252");
int zahlen[]={1,4,5,1,5,7,9,2,3,4};
int len = sizeof(zahlen)/sizeof(int);
int erg = array_unique(zahlen,len);
printf("Es wurden %d doppelte Zahlen gelöscht: \n",erg);
printf("Das Array hat nun folgende Werte: ");
printArrayUnique(zahlen,len);
return 0;
}
void printArrayUnique(int *array, int len){
for(int i=0; i<len; i++){
if(array[i]!=-1){
printf("%d ",array[i]);
}
}
}
int array_unique(int *array, int len){
int count=0;
for(int i=0; i<len;i++){
for(int j=i+1; j<len;j++){
if(array[i]==array[j]){
array[j] = -1;
count++;
}
}
}
return count;
}
I have not figured out any other solution to fix the faulty value of count.
The issue is due to the fact that your are counting duplicates more than once; so, when you have found a duplicate entry, you correctly replace that with -1 but then, later in the loops, you will be (potentially, at least) comparing two or more of those -1 values.
Just add a check that either value is not -1 (along with the test for equality) before incrementing the count variable:
int array_unique(int* array, int len)
{
int count = 0;
for (int i = 0; i < len; i++) {
for (int j = i + 1; j < len; j++) {
if (array[i] == array[j] && array[j] != -1) {
array[j] = -1;
count++;
}
}
}
return count;
}
Note also that, as mentioned in the comments, you really do need declarations of your functions before you use them. Add the following two lines before the main function:
void printArrayUnique(int* array, int len);
int array_unique(int* array, int len);
I'm new to C programming and I've run into a problem when creating 2D array printing function. When I try to execute the code below I get:
points.c:13: error: unknown array element size
As I've checked there are very similar codes online, which are supposed to work. I've tried to initialize function as
int print2DArray( int arrayLen, int elementLen, int array[arrayLen][elementLen])
but it raises:
points.c:3: error: 'arrayLen' undeclared
Could somebody tell me what's wrong with this code and how to fix it? I also don't understand why very similar function for 1D arrays works just fine. It has to be in pure C.
#include <stdio.h>
//supposed to print 2D array:
int print2DArray(int array[][], int arrayLen, int elementLen)
{
int i;
int j;
for (i = 0; i < arrayLen; i++)
{
for (j=0; j < elementLen; j++)
{
printf("%5d", array[i][j]);
}
printf("\n");
}
}
//prints 1D array:
int printArray( int array[], int arrayLen)
{
int i;
for (i = 0; i < arrayLen; i++)
{
printf("%d", array[i]);
}
}
--- edit ---
I undestand most of you pointed out that the function has to be called like that:
#include <stdio.h>
int print2DArray( int arrayLen, int elementLen, int array[arrayLen][elementLen])
{
int i;
int j;
for (i = 0; i < arrayLen; i++)
{
for (j=0; j < elementLen; j++)
{
printf("%5d", array[i][j]);
}
printf("\n");
}
}
This raises an error:
points.c:3: error: 'arrayLen' undeclared
I'm using tcc for windows and according to documentation it is supposed to support C99 VLA.
It appears OP's compiler (or the mode it is used) does not support variable length array (VLA) as a function parameter.
Below is a non-VLA approach.
void print2DArrayX(int arrayLen, int elementLen, const int *array) {
int i;
int j;
for (i = 0; i < arrayLen; i++) {
for (j = 0; j < elementLen; j++) {
printf("%5d", array[i*elementLen + j]);
}
printf("\n");
}
}
Call with address of first int, not the 2D array
#define ARRAY_LEN 3
#define ELEMENT_LEN 4
int array[ARRAY_LEN][ELEMENT_LEN] = { 0 };
...
print2DArrayX(ARRAY_LEN, ELEMENT_LEN, array[0]);
Ok, so thanks for all the answers - they were very helpful. I've just tried to use gcc in linux and as you've pointed out this approach works fine:
int print2DArray( int arrayLen, int elementLen, int array[arrayLen][elementLen])
I guess tcc (tiny c compiler, windows version 0.9.27) doesn't support VLA after all. A bit strange since documentation says it does.
How about you try this solution.
#include <stdio.h>
int print2DArray(int* array, int arrayLen, int elementLen)
{
int i;
int j;
for (i = 0; i < arrayLen; i++)
{
for (j=0; j < elementLen; j++)
{
printf("%5d ", *(array+j+elementLen*i));
}
printf("\n");
}
}
int main(){
int arr[2][6] = { {9,258,9,96,-8,5},
{1,1212,-3,45,27,-6}
};
print2DArray(*arr,2,6);
return 0;
}
Unless you are using a C99 compiler,
int print2DArray( int arrayLen, int elementLen, int array[arrayLen][elementLen])
is not possible.
Even if you are using C99 compiler, your code has a problem. You need to pass one of the dimension first.
int print2DArray(int arrayLen, int elementLen, int arr[][elementLen]);
So,
int print2DArray(int arrayLen, int elementLen, int arr[][elementLen])
{
// Your code
int i;
int j;
for (i = 0; i < arrayLen; i++)
{
for (j=0; j < elementLen; j++)
{
printf("%5d", array[i][j]);
}
printf("\n");
}
return 0;
}
This can be used as
int main(void)
{
int i32Array[3][3] = {{-15, 4, 36}, {45, 55, 12}, {-89, 568, -44568}};
int m = 3, n = 3;
// I am not sure why 'print2DArray' would return an int
// (or anything at all for that matter).
// If you can establish a case for it,
// modify the function and the value it is supposed to return,
// And catch it below.
print2DArray(m, n, i32Array);
return 0;
}
I am not sure how you are calling print2DArray function. Unless you post that piece of code, it is difficult to resolve your problem. Confirm that you are calling the function correctly as shown above.
I am hoping to compare two array and print two scores.
In the case below, should be 1 and 5 but I got 6488164 and 7536740. (as the first one only 7 is bigger than 4 and the next row is everything bigger)
Is it possible to compare a two-dimensional array with a single array and create an array with it?
What did I do wrong or what should I do in order to do the comparison?
#include<stdio.h>
#include<stdlib.h>
int
main(int argc, char *argv[]) {
int mm_avg[2][5] = {{1,2,3,7,4},{2,3,4,5,7}};
int lt_avg[5]={1,2,3,4,5};
int i, j, score[100];
for (i=0; i<5; i++){
for (j=0; j<2; j++){
if(mm_avg[j][i]>lt_avg[i]){
score[j]++;
}
}
}
for (j=0; j<2; j++){
printf("%d\n", score[j]);
}
return 0;
}
The score array is not initialized, so all 100 values in the array are just whatever happens to be lying around in memory.
Try int i, j, score[100] = {0};. This will initialize all 100 values to 0.
In C/C++, integers that are not initialized have an undefined value. Unlike say for instance, Java, which will assign a default value of 0 to an integer.
In general it is good practice to always explicitly initialize your objects when declared.
#include<stdio.h>
#include<stdlib.h>
main(int argc, char *argv[])
{
int mm_avg[2][5] = {{1,2,3,7,4},{2,3,4,5,7}};
int lt_avg[5]={1,2,3,4,5};
int i, j, score[2];
for(int ndx = 0; ndx < 2; ++ndx)
{
score[ndx] = 0;
}
for (i = 0; i < 5; ++i)
{
for (j = 0; j < 2; ++j)
{
if(mm_avg[j][i] > lt_avg[i])
{
/*printf("%d\n", j);
printf("%s", "mm_avg: ");
printf("%d\n", mm_avg[j][i]);
printf("%s", "lt_avg: ");
printf("%d\n", lt_avg[i]);
*/
score[j]++;
}
}
}
for (j=0; j<2; j++)
{
printf("%d\n", score[j]);
}
return 0;
}
#include <stdio.h>
int main(){
void sorting(){
int a[4];
a[0]=1;
a[1]=6;
a[2]=15;
a[3]=3;
a[4]=19;
int size = 4;
int t =1;
if (size ==0) return; // ie if you reach to the end stop
int i;
for (i=0;i<size-1;i++){
if(a[i+1] >a[i]) { //if the +1 element is bigger than before it do the swap
int j;
j= a[i+1];
a[i+1]=a[i]; //swap
a[i] = j; //swap
}
}
sorting(*a,size - 1);//recursion
void print_int() {
int i; // Loop counter
for (i = 0; i < 4; i++) {
printf("%d\n", a[i]);
}}
}
It compiles ok but when I try to run the file nothing appears? My intentions were to create an array sort them then display them.
Also, the code where the recursion happened "sorting(*a,size - 1);//"
if I tried to replace *a with a[] an error will happen. Why is that?
the error is "error expected expression before ']' token"!
thank you.
int a[4];
But you access a[4]=19; index 4 that is out of bound. You can access highest index 3.
I think function void sorting() should be defined outside main .Nested functions are GNU extensions in GCC.
Your code has to many problems. Here is a working Array sort:
#include <stdio.h>
void bubble_sort(int *array, int length){
int i,j, k, temp;
for (i = 0 ; i < length-1; i++){
for (k = 0 ; k < length-i-1; k++){
if (array[k] > array[k+1]){
temp = array[k];
array[k] = array[k+1];
array[k+1] = temp;
}
}
}
printf("The sorted Array List:\n\n");
for ( j = 0 ; j < length ; j++ ){
printf("%d ", array[j]);
}
}
int main(void){
int array[] = {1,6,15,3,19};
int length = sizeof array / sizeof array[0];
bubble_sort(array, length);
printf("\n");
return 0;
}
You should read about functions declarations and definitions.
About arrays you should know that if you declare:
int array[4];
Your working array is from 0 to 3 and not from 0 to 4.
Take a look at the following:
int main(void){
int array[] = {1,6,15,3,19};
int size = 5;
int i;
for(i=0;i<size;i++){
printf("%d ",array[i]);
}
return 0;
}
I have size=5 and not size=4- like you tried. You should be careful about number of Array elements.
Aside from all the problems spotted by others, you must repeatedly execute the for loop until no more exchanges are made, which is the standad way of bubbling. As you use recursion, it is of course nonsense to declare the array to be sorted (and its size) inside the function called recursively.
I need to create a function that takes a matrix and returns it transpose. The only requirement is that it directly returns a matrix, not just modifies it by reference. Here's what I've done so far:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define ROW 100000000
#define COL 100000000
int (*(f_MatTrans)(int mat[][COL], int r, int c))[COL];
int main(void)
{
int x[2][2]={1,2,3,4};
int (*a)[2];
a=f_MatTrans(x,2,2);
for(int i=0; i<2; i++)
{
for(int j=0; j<2; j++)
{
printf("X[%d][%d]=%d\n",i,j,x[i][j]);
printf("A[%d][%d]=%d\n",i,j,a[i][j]);
}
}
return 0;
}
int (*(f_MatTrans)(int mat[][COL], int r, int c))[COL]
{
int a[c][r];
for(int i=0; i<r; i++)
{
for(int j=0; j<c; j++)
{
a[j][i]=mat[i][j];
}
}
return a;
}
The purpose of this is to include the function on a library created by myself, just in case it is useful information.
The code in the question (when I read it) doesn't compile because the array x is not compatible with the function signature.
I'm not clear what the real constraints on your problem are. The easy way to do it in C99 or C11 is with VLA notation:
#include <stdio.h>
static void MatrixTranspose(int r, int c, int src[r][c], int dst[c][r])
{
for (int i = 0; i < r; i++)
for (int j = 0; j < c; j++)
dst[j][i] = src[i][j];
}
int main(void)
{
int x[3][2] = { { 0, 1 }, { 2, 3 }, { 4, 5 } };
int y[2][3];
MatrixTranspose(3, 2, x, y);
for (int i = 0; i < 3; i++)
{
for (int j = 0; j < 2; j++)
{
printf("X[%d][%d]=%d ", i, j, x[i][j]);
printf("Y[%d][%d]=%d\n", j, i, y[j][i]);
}
}
return 0;
}
Sample output:
X[0][0]=0 Y[0][0]=0
X[0][1]=1 Y[1][0]=1
X[1][0]=2 Y[0][1]=2
X[1][1]=3 Y[1][1]=3
X[2][0]=4 Y[0][2]=4
X[2][1]=5 Y[1][2]=5
My suspicion is that you are supposed to be doing something different (notationally more complex), but it is not yet clear what.
You cannot return a pointer to the local array, because that ceases to exist when the function returns. If you want your function to create the result array (not write to some other array that is passed into the function), you must use malloc() in these cases:
//The return type is actually `int (*)[r]`, but C doesn't like that.
int* f_MatTrans(int r, int c, int mat[][c]) {
int (*a)[r] = malloc(c*sizeof(*a));
for(int i=0; i<r; i++) {
for(int j=0; j<c; j++) {
a[j][i]=mat[i][j];
}
}
return *a;
}
Note that I changed the array types: If you declare mat as int mat[][COL], the number COL will be used to calculate the offset mat[1][0], which will be 100000000 integers after the first element in your case, while the array that you pass in only contains four integers. This is undefined behavior, and your program is allowed to format your harddrive if you do this.
Unfortunately, it is not possible for the type of the returned pointer to depend on the value of an argument to the function. That is why I changed the return type to a plain integer pointer, you must document that this is meant to be a pointer of type int (*)[r].
You would use the function above like this:
int main(void) {
int x[2][3]={1,2,3,4,5,6};
int (*a)[2] = (int (*)[2])f_MatTrans(2, 3, x);
for(int i=0; i<2; i++) {
for(int j=0; j<2; j++) {
printf("X[%d][%d]=%d\n",i,j,x[i][j]);
printf("A[%d][%d]=%d\n",i,j,a[i][j]);
}
}
free(a); //Cleanup!
return 0;
}