I have this piece of code that is supposed to sum all the even numbers but it isnt working
int n, k = 0, sum = 0;
for (i = 0; i < n; i++)
if (s[i] % 2 == 0) {
k++;
for (int i = 0; i < n; i++)
sum += s[i];
printf("%i ", s[i]);
}
printf("\n sum of even numbers=%i", sum);
int i, sum = 0;
for (i=0; i < n; i++) //n is the number of elements in the array
{
if (s[i] % 2 == 0)
sum = sum + s[i];
}
printf("Sum of the even numbers = %d",sum);
There was no need for a nested loop. Just delete the inner for
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);
}
Im taking a C programming beginning course, and have a problem with a for loop.
I want to make two double arrays. One that takes input from user, and one that sums the inputs.
I then want to output the two arrays. One that shows the input, and one that shows the sums og the input in every cell.
The problem comes when I try to show the sum for every "cell" in the array.
The output just becomes the same as the input.
I can solve it with:
// print all the numbers in the second array
for (i = 0; i < n; i++) {
sum = sum + a[i];
printf("%lf ", sum);
but then the assignment wouldn't be solved. Hope you can educate me.
#include <stdio.h> #include <stdlib.h>
int main(void) {
int n; //numbers of cells
int i; //The numbers in the cells
printf("How many cells in the array would you like? \n");
scanf("%d", &n);
double a[n], sum=0; // declare an array and a loop variable.
double b[n], sumo=0;
printf("Enter the numbers:\n");
for (i = 0; i < n; i++) { // read each number from the user
scanf("%lf", &a[i]);
}
printf("The results, my lord:\n");
// print all the numbers in the first array
for (i = 0; i < n; i++) {
printf("%lf ", a[i]);
}
printf("\n"); //THIS IS WHERE THE PROBLEM STARTS
// print all the numbers in the second array
for (i = 0; i < n; i++) {
b[i] = b[i] + a[i];
printf("%lf ", b[i]);
}
return 0;
}
For starters the array b is not initialized
double b[n], sumo=0;
So this statement
b[i] = b[i] + a[i];
invokes undefined behavior.
It seems what you need is the following for loop
for (i = 0; i < n; i++) {
b[i] = a[i];
if ( i != 0 ) b[i] += a[i-1];
printf("%lf ", b[i]);
}
You can calculate the sum (aka the b array) when you read the user data:
for (i = 0; i < n; i++)
{
scanf("%lf", &a[i]);
if (i == 0)
{
b[i] = a[i];
}
else
{
b[i] = b[i-1] + a[i];
}
}
or do it like:
scanf("%lf", &a[0]);
b[0] = a[0];
for (i = 1; i < n; i++)
{
scanf("%lf", &a[i]);
b[i] = b[i-1] + a[i];
}
or do it like:
sum = 0;
for (i = 0; i < n; i++)
{
scanf("%lf", &a[i]);
sum += a[i];
b[i] = sum;
}
The last part is how I solved the problem. I found the issue that. I didn't update the "sum" for ever loop. It adds a new value in b[I] this way. :-)
double a[n], sum=0; // declare an array and a loop variable.
double b[n];
printf("Enter the numbers:\n");
for (i = 0; i < n; i++) { // read each number from the user
scanf("%lf", &a[i]);
}
printf("The results, my lord:\n");
// print all the numbers in the first array
for (i = 0; i < n; i++) {
printf("%.2lf ", a[i]);
}
printf("\n");
// print all the numbers in the second array
for (i = 0; i < n; i++) {
sum = sum + a[i];
b[i] = sum;
printf("%.2lf ", b[i]);
I am doing the following problem:
Giving the sequence a consisting of n integer numbers and the sequence b consisting of m integer numbers, two sequences are arranged in increasing order. Combining two above sequences into a new sequence c such that c is also an increasing sequence. Printing c.
Input:
3
1 3 4
4
1 2 3 5
Output:
1 1 2 3 3 4 5
My idea is first combining two sequences into sequence c, then sorting sequence c in increasing order. This is my code:
#include <stdio.h>
int main() {
//Inputting sequence a and b
int n, m;
int a[1001], b[1001];
scanf("%d", &n);
for (int i = 0; i < n; i++) {
scanf("%d", &a[i]);
}
scanf("%d", &m);
for (int i = 0; i < m; i++) {
scanf("%d", &b[i]);
}
//Combine two sequence into c
int c[1001];
for (int i = 0; i < n; i++) {
c[i] = a[i];
}
for (int i = 0; i < m; i++) {
c[i + n] = b[i];
}
//Arrange sequence c in increasing order
int mid;
for (int i = 0; i < (n + m - 1); i++) {
for (int j = 1; j < (n + m); j++) {
if (c[i] > c[j]) {
mid = c[i];
c[i] = c[j];
c[j] = mid;
}
}
}
//Printing c
for (int i = 0; i < (n + m); i++) {
printf("%d ", c[i]);
}
return 0;
}
However, when I test with the test case [1,2,4],[1,2,5], the result is 1 4 2 2 1 5. Can anyone point out the error in my code? I truly appreciate that.
It is wrong to search for the minimum value in the range of 1 to n+m-1 regardless of the value i. This may move the minimum value to the latter part of the array.
The line
for (int j = 1; j < (n+m); j++)
should be
for (int j = i + 1; j < (n+m); j++)
To merge 2 sorted arrays, you can write 3 loops as in the classic implementation of mergesort:
#include <stdio.h>
int main() {
//Inputting sequence a and b
int a[1000], b[1000], c[2000];
int n, m, i, j, k;
if (scanf("%d", &n) != 1 || n <= 0 || n > 1000)
return 1;
for (i = 0; i < n; i++) {
if (scanf("%d", &a[i]) != 1)
return 1;
}
if (scanf("%d", &m) != 1 || m <= 0 || m > 1000)
return 1;
for (i = 0; i < m; i++) {
if (scanf("%d", &b[i]) != 1)
return 1;
}
//Combine both sequences into c
i = 0, j = 0, k = 0;
while (i < n && j < m) {
if (a[i] <= b[j])
c[k++] = a[i++];
else
c[k++] = b[j++];
}
while (i < n) {
c[k++] = a[i++];
}
while (j < m) {
c[k++] = a[j++];
}
//Printing c
for (i = 0; i < n + m; i++) {
printf("%d ", c[i]);
}
printf("\n");
return 0;
}
My task is: If we look at any two neighbour values in an array, if the one on the right is two times greater than the one on the left, their average should be inserted between them and the new array consisting of old and new elements should be printed. I have a problem with moving the other elements after average.And using special functions or libraries is not allowed.I am beginner, and I hope you could help.
#include <stdio.h>
int main() {
int n, i, j;
double a[100], average;
printf("Enter the number of elements: ");
scanf("%d", &n);
for (i = 0; i < n; i++) {
scanf("%lf", &a[i]);
}
for (i = 0; i < n; i++) {
if ((a[i + 1] / a[i]) == 2) {
for (i = j = 0; i < n; ++i)
b[j++] = a[i];
if (a[i + 1] / a[i] == 2)
average = (a[i + 1] + a[i]) / 2;
b[j++] =average;
}
}
for (i = 0; i < j; ++i) {
printf("%lf\n", b[i]);
}
}
A simple way to solve your problem is adding double b[199];, and copying everything over:
for (i = j = 0; i < n; ++i) {
b[j++] = a[i];
if (...) b[j++] = ...; /* Append the average to b. */
}
for (i = 0; i < j; ++i) {
printf("%lf\n", b[i]);
}
If you really want to move the elements forward within a itself, then you can do it by adding an inner for loop (and an additional loop variable int k;) which copies the elements one-by-one:
for (k = n++; k > i; --k) {
a[k] = a[k - 1];
}
In order to insert an element in an array, you must copy the elements with higher index from the last one down.
Also avoid dividing by a[i] that can be zero, and properly handle 0,0 that match the criteria for inserting the average, and skip the inserted value to avoid inserting more zeros.
#include <stdio.h>
#include <stdlib.h>
int main() {
int n, i, j;
printf("Enter the number of elements: ");
if (scanf("%d", &n) != 1 || n <= 0)
return 1;
double *a = malloc(sizeof(*a) * (2 * n - 1)); // allocate the array to the maximum size
if (a == NULL)
return 0;
for (i = 0; i < n; i++) {
if (scanf("%lf", &a[i]) != 1)
return 1;
}
for (i = 1; i < n; i++) {
if (a[i] == a[i - 1] * 2) {
for (j = n; j > i; j--)
a[j] = a[j - 1];
a[i] = (a[i - 1] + a[i]) / 2;
n++; // increase number of elements
i++; // skip the new value
}
}
for (i = 0; i < n; ++i) {
printf("%f\n", a[i]);
}
free(a);
return 0;
}
To insert an element in a specific position you would need to move the rest of the array. However doing it many times is expensive and you may prefer to use an array to store the position at which you want to insert the elements and then insert them all at once.
Alternatively you can create a new array where to copy the original plus the new values.
However there's an easier and faster way, that is adding the new values straight away, while you fill the original array. Here's a program that does that.
#include <stdio.h>
#define SIZE 100
int main() {
int i, n, avg = 0;
double a[SIZE];
while( puts("Enter the number of elements:") && (scanf("%d", &n) != 1 || n < 1 || n > SIZE) );
scanf("%lf", &a[0]);
for(i = 1; i < n+avg && i < SIZE-1 && scanf("%lf", &a[i]) == 1; i++) {
if( a[i] == a[i-1] * 2 ) {
a[i+1] = a[i];
a[i] = (a[i] + a[i-1]) / 2;
++avg;
++i;
}
}
for(i = 0; i < n+avg; i++) {
printf("%lf\n", a[i]);
}
return 0;
}
everyone!
I create matrix with random elements:
static int array[10][10];
int i, j, m, n, sum = 0;
printf("Enter the order of the matrix\n");
scanf("%d %d", &m, &n);
for (i = 0; i < m; ++i)
{
for (j = 0; j < n; ++j)
{
printf("%d ", rand() % 10);
}
printf("\n");
}
And this is one function to sum row elements:
for (i = 0; i < m; ++i)
{
for (j = 0; j < n; ++j)
{
sum = sum + array[i][j];
}
printf("Sum of the %d row is = %d\n", i, sum);
sum = 0;
}
My problem is that program wont to sum it properly, program just print 0 for result.
Also, when I add manual elements, program works fine, but wont with random numbers.
Someone to help me? Thank you!
You haven't actually assigned the values to the array; you're just printing them.
for (i = 0; i < m; ++i)
{
for (j = 0; j < n; ++j)
{
int num = rand() % 10;
printf("%d ", num);
array[i][j] = num;
}
printf("\n");
}
is probably what you want.
Also the array has space for only 10 x 10 elements. So you need to validate that the inputs for m and n do not exceed that limit.
The default value of int type in C is 0. Because you do not enter the value to array, so all of values of this array are equal to 0. So sum = 0 after all calculations.
Try to initialize values for this array. For example, in the first for loop (the for loop content printf with rand() function):
array[i][j] = rand() % 10;
OR
array[i][j] = 1; // or whatever you want