I'm trying to sort an array size in C, i have ran some tests on it before i publish it here (I have left the testing statement in).
I get the correct answer once but than it moves the higher value into the wrong array, even though i have used an IF statement.
If you guys run the program it will make sense to you.
#include <stdio.h>
# define size 3
int sum();
main() {
int a[size] = { 4, 2, 3 };
int temp, i, j, x;
for (j = 0; j < size; j++){
for (i = 1; i < size; i++){
for (x = 0; x < size; x++){
printf("%d", a[x]); //testing statement;
}
printf("\n");
if (a[j] > a[i]){
temp = a[j];
a[j] = a[i];
a[i] = temp;
}
}
}
for (x = 0; x < size; x++){
printf("%d", a[x]);
}
getch();
}
Change
for (i = 1; i < size; i++){
to something like
for (i = j + 1; i < size; i++) {
and your sort will work correctly. As it is, you're comparing the elements again with if (a[j] > a[i]){ which can move them back when you reset i to 1.
Related
Im trying to sort a matrix by the sum of its row's digits, from highest to lowest. I dont know if i explained that correctly so here's some photos explaining it.
This is what my code outputs. Basically, it asks you for m and n, which are the dimensions of the matrix. In this example it's a 3x4, 3 rows and 4 columns. Then, the matrix should be sorted by rows, by the sum of row's digits. Which means, instead of what's being outputted in the picture above, the correct result should be this:
I have no idea how to sort this from highest to lowest, i have been trying for hours to no avail.
Here's my code:
#include <stdio.h>
#define N 30
void main(){
double a[N][N], s[N], p;
int i, j, m, n, max;
while(1){
printf("\nm, n? ");
scanf("%d%d", &m, &n);
if(m <= 0 || m > N || n <=0 || n > N)
break;
for(i = 0; i < m; i++){
printf("%2d. row? ", i+1);
for(j = 0; j < n; scanf("%lf", &a[i][j++]));
}
for(i = 0; i < m; i++)
for(s[i] = j = 0; j < n; s[i] += a[i][j++]);
for(j = 0; j < n - 1; j++){
for(max = i, j = i+1; j < n; j++)
if(s[j] > s[max])
max = i;
if(max != j){
p = s[j];
s[j] = s[max];
s[max] = p;
for(j = 0; j < m; j++){
p = a[j][i];
a[j][i] = a[j][max];
a[j][max] = p;
}
}
}
printf("New matrix: \n");
for(i = 0; i < m; i++){
for(j = 0; j < n; printf("%8.2lf", a[i][j++]));
printf("\n");
}
for(j = 0; j < m; j++)
printf("-------------");
printf("\n");
for(j = 0; j < m; printf("%8.2f \n", s[j++]));
printf("\n");
}
}
You can sort the rows of the matrix from highest to lowest, using a simple bubble sort algorithm.Your code modified below:
int main() {
double a[N][N], s[N], p;
int i, j, m, n, max;
while (1) {
printf("\nm, n? ");
scanf("%d%d", & m, & n);
if (m <= 0 || m > N || n <= 0 || n > N)
break;
for (i = 0; i < m; i++) {
printf("%2d. row? ", i + 1);
for (j = 0; j < n; scanf("%lf", & a[i][j++]));
}
for (i = 0; i < m; i++)
for (s[i] = j = 0; j < n; s[i] += a[i][j++]);
for (i = 0; i < m - 1; i++) { // modified here
for (j = i + 1; j < m; j++) { // modified here
if (s[j] > s[i]) { // modified here
p = s[i];
s[i] = s[j];
s[j] = p;
for (int k = 0; k < n; k++) {
p = a[i][k];
a[i][k] = a[j][k];
a[j][k] = p;
}
}
}
}
printf("New matrix: \n");
for (i = 0; i < m; i++) {
for (j = 0; j < n; printf("%8.2lf", a[i][j++]));
printf("\n");
}
for (j = 0; j < m; j++)
printf("-------------");
printf("\n");
for (j = 0; j < m; printf("%8.2f \n", s[j++]));
printf("\n");
}
return 0;
}
Here's how i modified your code to achieve that:
Initialize a loop variable i to 0.
In the outer loop, run the inner loop j from i+1 to m-1.
In the inner loop, compare the sum of the row i with the sum of row
j. If the sum of row j is greater than the sum of row i, swap the
rows using a temporary variable.
After the inner loop finishes, increment the value of i by 1. Repeat
the outer loop until i becomes equal to m-1.
Output:
You can just use qsort to let it handle the sorting and item swapping. Then you only need to write the code for comparing two rows with each other.
Given something like this:
int matrix[3][4] =
{
{1,2,3,4},
{5,6,7,8},
{9,1,2,3},
};
You'd call qsort as:
qsort(matrix, 3, sizeof(int[4]), compare);
The only complexity is implementing the comparison callback function. There's two things to consider there:
We've told qsort that we have an array of 3 items, each of type int[4]. So the void pointers it passes along to us will actually be pointers to type int[4]. That is: int(*)[4].
qsort sorts in ascending order by default, where the item considered "less" ends up first. So we need to tweak that to get the largest item first.
Example:
int compare (const void* obj1, const void* obj2)
{
const int (*ptr1)[4] = obj1;
const int (*ptr2)[4] = obj2;
size_t sum1=0;
size_t sum2=0;
for(size_t i=0; i<4; i++)
{
sum1 += (*ptr1)[i];
sum2 += (*ptr2)[i];
}
if(sum1 > sum2) // largest sum considered "less" for qsort
return -1;
else
return 1;
return 0;
}
sum1 < sum2 would have placed the smallest row first.
Full example:
#include <stdio.h>
#include <stdlib.h>
int compare (const void* obj1, const void* obj2)
{
const int (*ptr1)[4] = obj1;
const int (*ptr2)[4] = obj2;
size_t sum1=0;
size_t sum2=0;
for(size_t i=0; i<4; i++)
{
sum1 += (*ptr1)[i];
sum2 += (*ptr2)[i];
}
if(sum1 > sum2) // largest sum considered "less" for qsort
return -1;
else
return 1;
return 0;
}
void print_matrix(size_t col, size_t row, int matrix[col][row])
{
for(size_t i=0; i<col; i++)
{
for(size_t j=0; j<row; j++)
{
printf("%d,", matrix[i][j]);
}
puts("");
}
}
int main (void)
{
int matrix[3][4] =
{
{1,2,3,4},
{5,6,7,8},
{9,1,2,3},
};
print_matrix(3,4,matrix);
puts("");
qsort(matrix, 3, sizeof(int[4]), compare);
print_matrix(3,4,matrix);
}
I want to randomize a to p without repetition.
int main(){
int array2[4][4];
bool arr[100]={0};
int i;
int j;
srand(time(NULL));
for(i=0; i<=3; i++){
for(j=0; j<=3; j++){
int randomNumber1;
randomNumber1 = (rand() % (82-65+1))+65;
if (!arr[randomNumber1])
{
printf("%c ",randomNumber1);
array2[i][j]=randomNumber1;
}
else
{
i--;
j--;
arr[randomNumber1]=1;
}
}
printf("\n");
}
return;
the output still has repeat alphabet. I want to have the output in 4x4 with with all a to p without it repeating.
There are some errors in your code. IMHO the most serious is that arr[randomNumber1]=1; is is the wrong branch of the test. That means that your current code does not invalidate once a number was used but only if it has already been invalidated => if you control the arr array at the end of the program all value are still 0.
That is not all. When you get a duplicate, you should only reset the inner loop, and you are currently off by 2 in your maximum ascii code: you go up to R when you want to stop at P.
Your code should be:
for (i = 0; i <= 3; i++) {
for (j = 0; j <= 3; j++) {
int randomNumber1;
randomNumber1 = (rand() % (81 - 65)) + 65;
if (!arr[randomNumber1])
{
printf("%c ", randomNumber1);
array2[i][j] = randomNumber1;
arr[randomNumber1] = 1;
}
else
{
//i--;
j--;
}
}
printf("\n");
}
But this kind of code is terribly inefficient. In my tests it took 30 to 60 steps to fill 16 values, because random can return duplicates. This is the reason why you were advised in comments to use instead the modern algorithm for Fisher-Yates shuffle:
int main() {
int array2[16];
unsigned i, j, k=0;
// initialize array with alphabets from A to P
for (i = 0; i < sizeof(array2); i++) {
array2[i] = 'A' + i;
}
// Use Fisher-Yates shuffle on the array
srand(time(NULL));
for (i = 15; i > 0; i--) {
j = rand() % (i + 1);
if (j != i) {
int c = array2[i];
array2[i] = array2[j];
array2[j] = c;
}
}
// Display a 4x4 pattern
for (i = 0; i < 4; i++) {
for (j = 0; j < 4; j++) {
printf("%c ", array2[k++]);
}
printf("\n");
}
return 0;
}
Which shuffles the array in only 16 steps.
Here is the outline
// Need some #includes here - exercise for the reader
char items[] = "abcdefghijklmnopqrstuvwxyz";
int len = sizeof(items);
srand(time(NULL));
while (len > 0) {
int r = rand() % len;
printf("%c", items[r]);
len--;
items[r] = items[len];
}
This should do the trick to print the whole alphabet in random order without repeats. Modify to do what you need it to do
I wrote to program in C to attempt to print array elements in descending order. I wrote a nested loop which would find the maximum element of the array and the value of the element would be set to later 0. This process would be repeated for all the elements. However, in the output, I am getting the first 2-3 values as desired but the remaining values are garbage. Any suggestions?
int main() {
int i, j, n, k;
scanf("%d\n", &n);
int a[100], b[100];
for (i = 0; i < n; i++) {
scanf("%d", &a[i]);
}
for (i = 0; i < n; i++) {
int max = a[i];
for (j = i; j < n; j++) {
if (a[j] > max) {
max = a[j];
b[i] = max;
}
}
for (k = 0; k < n; k++) {
printf("%d", a[k]);
if (a[k] == b[i]) {
a[k] = 0;
}
}
printf("\n");
}
for (i = 0; i < n; i++) {
printf("%d ", b[i]);
}
}
The main issue is that you only set b[i] = max; when you find a new max, but since you initialized max to be a[i] it could happen that it already holds the maximum value. So the if never executes, therefore b[i] is not written and there's garbage value in it. You should move this line from the if after that for loop.
Another issue is that you initialize j with i in this loop. You should initialize it to 0.
The changed part:
for (j = 0; j < n; j++) {
if (a[j] > max) {
max = a[j];
}
}
b[i] = max;
I'm new to C and I'm just trying to print out a two 2 array.
This bug has been annoying me all day and I'm not really sure whats going on.
#include<stdio.h>
void run(int);
main()
{
run(5);
return 0;
}
//Have to make it a character array as it needs to
//store numbers AND commas.
run(int x)
{
int size = 2*x -1;
char array[size][size];
int i = 0;
int j = 0;
for( i; i < size; i++){
for(j; j< size; j++){
array[i][j] = '1';
}
}
int k = 0;
int l = 0;
for( k; k < size; k++){
for(l; l< size; l++){
printf( "%c" , array[l][k]);
}
printf("%\n", "");
}
}
This is the output I get:
1%
%
%
%
%
%
%
%
%
You code has several mistakes:
The biggest problem is that your not initializing your loop counters where you should:
for(i; i < size; i++){
for(j; j < size; j++){
With that, i & j are left as they were prior to the for statement. The first section of these statements does nothing at all. While that's harmless for i (since it's initialized to 0 before the for), that's devastating for j, which never goes back to 0. Your code should be:
for(i = 0; i < size; i++){
for(j = 0; j < size; j++){
The same issue exists with k & l, and the same fix should be applied:
for(k = 0; k < size; k++){
for(l = 0; l < size; l++){
Next, you're "rotating" access in your array. When you fill the array with values, you have i in your outer loop and j in the inner loop, and you use them as [i][j]:
array[i][j] = '1';
Think of that as Out & In --> [Out][In].
When you print the array, you "rotate" that, k is outer & l is inner, and you use them as [l][k]:
printf("%c", array[l][k]);
That's like doing [In][Out].
While that's not a problem with all values being identical ('1'), and the matrix being square (width == height), it won't work with other values or dimensions, and is confusing.
Last, you're attempt to print a new line is wrong. You have a % specifier, but your not really using any valid character after that, and you don't need that anyway, just print:
printf("\n");
So, all together, here's what the code should be:
run(int x)
{
int size = 2*x -1;
char array[size][size];
int i,j;
for(i = 0; i < size; i++){
for(j = 0; j < size; j++){
array[i][j] = '1';
}
}
int k, l;
for(k = 0; k < size; k++){
for(l = 0; l < size; l++){
printf("%c", array[k][l]);
}
printf("\n");
}
}
(And as a side note, k & l are not really required, you can simply reuse i & j)
Can anyone explain why this bubble sort function doesn't work and why I lose numbers in my output? I'm very new to C, so please forgive me if this is something very obvious I have missed.
#include <stdio.h>
#include <stdlib.h>
int bubble(int array[],int length) {
int i, j;
int temp;
for(i = 0; i < (length); ++i) {
for(j = 0; j < (length - 1); ++j) {
if(array[i] > array[i+1]) {
temp = array[i+1];
array[i+1] = array[i];
array[i] = temp;
}
}
}
return 0;
}
int main() {
int array[] = {12,234,3452,5643,0};
int i;
int length;
length = (sizeof(array)/sizeof(int));
printf("Size of array = %d\n", length);
bubble(array, length);
for (i = 0; i < (length); ++i) {
printf("%d\n", array[i]);
}
return 0;
}
Output
Size of array = 5
12
234
3452
0
0
In your inner loop, you don't use j at all. Double check your logic.
Also note that array[i+1] goes beyond the array boundary.
for (i = 0; i < (length-1); ++i) {
for (j = 0; j < (length-i-1); ++j) {
if(array[j] > array[j+1]) {
temp = array[j+1];
array[j+1] = array[j];
array[j] = temp;
}
}
}
In a bubble sort you only use the inner loop variable.
Another thing, the inner loop goes from 0 to i if I remember well; but I think that's just an optimisation (as the tail is remains sorted in each step).
Try to run step by step your code with paper and pencil. That always works.
for (i = 0; i < (length); i++) {
for (j = 1; j < (length-i); j++) {
if(array[j-1] > array[j]) {
temp = array[j-1];
array[j-1] = array[j];
array[j] = temp;
}
}
}