I've been stuck on this problem for ages now and don't seem to know how to complete this program. I am a beginner in programming so I only know C. I will admit this is for an assignment and I am not looking for the answer but I would really appreciate a little help with the problem. This is what I have:
#include <stdio.h>
#include <math.h>
void main()
{
int low, high, n, count,i;
scanf ("%d %d",&low, &high);
count=0;
n=0;
if (low<=3)
count=count+1;
while (n<low)
{
n=n+6;
}
while (n<high)
{
i=1;
while (i<sqrt(n+1))
{
i=i+2;
if ((n-1)%i==0 || (n+1)%i==0)
continue;
else
count=count+1;
}
n=n+6;
}
printf("the number of twin primes between %d and %d are %d",low, high, count);
}
Am I using while loops wrong and/or the if statements? I haven't been taught to use for loops so I can't use those. I also have to use the fact that every twin prime besides {3,5} follow the formula 6+/-1.
Thank you for helping me.
The following program work correctly.
#include <stdio.h>
#include <math.h>
int main(int argc, char *argv[])
{
int low, high, n, count, i;
scanf ("%d %d", &low, &high);
count = 0;
n = 0;
if (low <= 3)
count++;
while (n<low)
n += 6;
while (n < high) {
i = 1;
int flag = 0;
while (i * i < n + 1) {
i++;
if ((n - 1) % i == 0 || (n + 1) % i == 0)
flag = 1;
}
if (!flag)
count++;
n += 6;
}
printf("the number of twin primes between %d and %d are %d", low, high, count);
}
as you can see you need just something like flag for your prime detection phase.
Related
I have to find a missing number in a sequence of numbers.
The input consists of a positive integer n, between 0 and 35000, and n unique numbers with range [0..n]. (So this range contains n+1 numbers).
I already tried some things with sum={n*(n+1)}/2 and then misNum=sum-SumOfNum;, but I couldn't find a way to make this work.
I wrote some code, but not with the examples I mentioned before. Obviously, this code is not complete, but I don't know how to make it complete.
#include <stdio.h>
#include <stdlib.h>
int main (int argc, char *v[]) {
int length;
int num;
scanf("%d", &length);
/*scanf(???)*/
int goal=length;
int i;
for(i=0; i!=length; i++){
goal=goal+i-num[i];
};
return goal;
}
Input and outcome should be:
Input: 2 "enter" 0 2. Output: 1
Input: 3 "enter" 0 3 1. Output: 2
Sum of all numbers from 0 to n is
n(a1+an)/2 = (in your case a1 = 0 and an = n+1) n*(n+1)/2
so the missing number is n*(n+1)/2 - (sum of input numbers after the length)
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char* v[]) {
int length;
int i = 0;
int sum = 0;
scanf_s("%d", &length);
// calculate arithmetic series sum
auto series_sum = ((length + 1) * (length)) / 2;
while (i < length)
{
int next;
scanf_s("%d", &next);
sum += next;
++i;
}
printf("missing num is %d ", series_sum - sum);
}
You have n number of integers to be scanned. Use mathematical equation to calculate the sum of first n+1 natural numbers. Then run a loop for n times and then run a loop to add all the n numbers scanned. Then subtract this sum with the sum of n+1 natural number. Result will be the missing number.
The calculation from the question is also correct and can be made to work with a few modifications.
#include <stdio.h>
#include <stdlib.h>
int main (int argc, char *v[]) {
int length;
int num;
// printf("enter maximum number: ");
scanf("%d", &length);
int goal=length;
int i;
for(i=0; i!=length; i++){
// printf("number[%d]: ", i);
if(scanf("%d", &num) != 1) {
fprintf(stderr, "invalid input\n");
return 1;
}
if((num < 0) || (num > length)) {
fprintf(stderr, "invalid number %d\n", num);
return 2;
}
goal=goal+i-num;
};
// printf("missing number: ");
printf("%d\n", goal);
return 0;
}
What am i doing wrong here?
#include<stdio.h>
int main(){
int i,count;
long long int sum = 0, num;
for(num = 1; num <= 1000; num++){
count = 0;
for(i = 2; i <= num / 2; i++){
if(num % i == 0){
count++;
break;
}
}
if(count == 0 && num != 1)
sum = sum + num;
}
printf("Sum of prime numbers is: %d ", sum);
return 0;
}
I tried to make a program that outputs the sum of all primes below nth number, n being 2 million however when i try to run it, there is a slight delay and it outputs nothing... it works well enough for small numbers like 1000 or 100 but big numbers it just does not output anything.There are no error or bugs that i know of either. (please help, i know nothing, so guide this young one)
The above program is fine, but it is possible to further reduce the time complexity and make it faster. The better approach is to use sieve of eratosthenes algorithm.You can read about it here http://www.geeksforgeeks.org/sieve-of-eratosthenes/
The program for your problem is
#include <bits/stdc++.h>
using namespace std;
void SieveOfEratosthenes(long long int n)
{
bool prime[n+1];
memset(prime, true, sizeof(prime));
for (long long int p=2; p*p<=n; p++)
{
if (prime[p] == true)
{
for (int i=p*2; i<=n; i += p)
prime[i] = false;
}
}
long long sum=0;
for (int p=2; p<=n; p++)
if (prime[p])
sum+=p;
cout << sum << " ";
}
int main()
{
int n = 2000000;
cout << "sum of prime numbers less then 2000000 is :" << endl;
SieveOfEratosthenes(n);
return 0;
}
Please let me know if you face difficulty in understanding the program.Note: You can also use Segmented seive to further reduce the time complexity
#include<stdio.h>
#include<math.h>
int main(){
int i,count;
long long int sum=0, num;
for(num = 1;num<=1000000;num++){
count = 0;
for(i=2;i<=sqrt(num);i++){ //change here
if(num%i==0){
count++;
break;
}
}
if(count==0 && num!= 1)
sum = sum + num;
}
printf("Sum of prime numbers is: %lld ",sum); //and here
return 0;
}
Some simple maths, while checking for prime, check up to square root of a number. And in printf() the format specifier for long long int is %lld not %d.
#include "stdafx.h"
#include "stdio.h"
#include <string.h>
void main() {
int Results[8];
int i = 0;
int max = 0;
int maxindex;
printf("Enter the results of your 7 leavin cert subjects: ");
do {
printf("\nSubject %d: ", i + 1);
scanf_s("%d", Results);
i++;
} while (i < 7);
for (i < 7; Results[i] > 0; i++)
if (Results[i] > max)
max = Results[i];
printf("The best grade is %d", max);
}
Hello, so basically I'm trying to print out the largest number(Best result) by using a for loop. However it keeps telling me the that the best result is 0.
Does anybody know what I'm doing wrong. Any help would be greatly appreciated.
There are 2 major problems in your code:
You read all numbers into Results[0] with the scanf_s("%d", Results);. You should instead write:
if (scanf_s("%d", &Results[i]) != 1) {
/* not a number, handle the error */
}
The second loop is incorrect: for (i < 7; Results[i] > 0; i++) has multiple issues. Write instead for (i = 0; i < 7; i++)
And smaller ones too:
#include "stdio.h" should be written #include <stdio.h>
#include "stdafx.h" is not used, and so can be removed - regardless, it should be written as #include <stdafx.h> if it were to be used.
The Results array has size 8, but you only use 7 slots.
main should have prototype int main(void) or int main(int argc, char *argv[]) or equivalent.
favor idiomatic for (i = 0; i < 7; i++) loops over error prone do / while loops.
use braces for a non trivial loop body.
Here is a simpler and better version:
#include <stdio.h>
#include <string.h>
int main(void) {
int Results[7];
int i, n, max;
printf("Enter the results of your 7 leavin cert subjects: ");
for (i = 0; i < 7; i++) {
printf("\nSubject %d: ", i + 1);
if (scanf_s("%d", &Results[i]) != 1) {
printf("invalid number\n");
exit(1);
}
}
for (n = i, max = 0, i = 0; i < n; i++) {
if (Results[i] > max)
max = Results[i];
}
printf("The best grade is %d\n", max);
return 0;
}
I would like to write a program which can find all prime numbers between two numbers in t test cases. But my program had crashed when I run it.
Please, could anyone help me?
My code:
#include <stdio.h>
#include <malloc.h>
#include <math.h>
void print(int a,int b)
{
int *p,i;
int x;
p = (int *) malloc (sizeof(int)*(b-a));
for(i=0;i<(b-a);i++) p[i]=a+i;
for(i=0;i<(b-a)/2;i++)
{
if(p[i]!=0)
{
if(p[i]%i==0) p[i]=0;
}
}
for(i=0;i<=(b-a);i++) if(p[i]!=0) printf("%d ",p[i]);
free(p);
}
int main(void)
{
int t,i,m,n;
scanf("%d",&t);
for(i=0;i<t;i++)
{
scanf("%d %d",&m,&n);
print(m,n);
}
return 0;
}
The problem is stumbling on allocating memory in a range, allocating one element too few (should have been malloc (sizeof(int)*(b-a+1));) and then not sticking to indexing the memory allocated. This could be so much simpler: no arrays needed - if a number has a divisor, there is no need to check any other divisors.
Sometimes it is easier to side-step the problems than struggle with them.
#include <stdio.h>
#include <math.h>
int prime(int n)
{
int s, i;
if (n == 1 || n == 2)
return 1;
if (n % 2 == 0) // no even numbers
return 0;
s = (int)sqrt(n); // limit the loop
for (i=3; i<=s; i+=2) // odd numbers only
if (n % i == 0)
return 0;
return 1;
}
void print(int a, int b)
{
int n;
for (n=a; n<=b; n++)
if (prime (n))
printf("%d ", n);
printf("\n");
}
int main(void)
{
int t, i, m, n;
printf("Input number of ranges to test: ");
scanf("%d", &t);
for(i=0; i<t; i++)
{
printf("Input bottom and top of range: ");
scanf("%d %d", &m, &n);
print(m, n);
}
return 0;
}
You messed up the termination of the for-loops. You allocated b-a bytes but you are iterating over b-a+1 items...
for(i=0;i<=(b-a);i++) p[i]=a+i;
needs to be a i<(b-a) or else you have a segfault (in both loops).
Also as BLUEPIX pointed out:
for(i=0;i<b/2;i++)
needs to be i<(b-a)/2 for iterating over half the intervall.
p[i]%i
Division by zero in the first iteration i==0.
After this the programm should terminate without an error.
I have to display the following figure (The two triangles intercept) for a n given by the user, where n is odd. The figure is in this link: http://i.imgur.com/mQxarLz.jpg
*******
*****
***
*
*
***
*****
*******
I already wrote this code, but I don't know how to give the n, where n is odd. And my code doesn't compile; it says: "In the fifth row, syntax error before for".
#include <stdio.h>
int main (void) {
int n,i,k,m;
for(m=0;m<2;m++)
for (i=1;i<=n;i++){
if(m==0){
for(k = 1; k<=n-i; k++){
printf(" ");
}
}
}
for (k=1;k<2*i;k++){
printf("%s","*");
//printf("%d",i);
}
scanf("%d",&n);
for (k = 1; k<=i;k++)
for (k=1;k<(n-i)*2;k++)
for (i=1;i<=n;i++) {
printf("\n$");
}
return 0;
}
First, the answer to "how do I check whether an integer is odd": you simply divide by 2 and check if the remainder is 0 (even) or 1 (odd). In C and most related languages, this is what the modulo operator "%" does:
if ((n % 2) == 1) {
// The number is odd.
}
But you should make sure that you read your n right at the start, because in the code that you have submitted, n is read in your second "for" loop before you have actually written something to it. And that means, n contains garbage at that point.
Good programming is to solve problems in the most simple way you can find. This particular algorithm is really fundamental stuff, thus you shouldn't end up with anything much more complicated than this:
#include <stdio.h>
#include <stdbool.h>
void print_chars (char symbol, int n)
{
for(int i=0; i<n; i++)
{
printf("%c", symbol);
}
}
void print_triangle (int base_size, int height, bool pointing_up)
{
int star_count = pointing_up ? 1 : base_size;
for(int row = 0; row < height; row++)
{
int spaces = base_size - star_count;
print_chars (' ', spaces/2);
print_chars ('*', star_count);
print_chars (' ', spaces/2);
printf("%\n");
star_count += pointing_up ? 2 : -2;
}
}
int main (void)
{
print_triangle(7, 4, false);
print_triangle(7, 4, true);
}
Note that the above code will behave strange if the triangle's base isn't in sync with its height - I left that out intentionally, feel free to improve the program further with such.
#include <stdio.h>
void printAsterisk(int n, int length){
int i, slen = (length - n)/2;
for(i=0;i < slen;++i)
putchar(' ');
for(i=0;i < n;++i)
putchar('*');
putchar('\n');
}
/* non-recursive
void printTriangle(int n, int length){//n isn't required as an argument
int d= -2;
for(; n < length + 1; n += d){
if(n < 0) n += (d *= -1);
printAsterisk(n, length);
}
}
*/
void printTriangle(int n, int length){
if(n < 1) return;
printAsterisk(n, length);
printTriangle(n - 2, length);
printAsterisk(n, length);
}
int main(void){
int n;
do{
printf("input odd number:");
scanf("%d", &n);
}while(n % 2 == 0);
printTriangle(n, n);
return 0;
}