void main() {
int low, high, odds = 0;
do {
printf("Please enter a number:");
rewind(stdin);
scanf("%d", &low);
} while (low <= 0);
do {
printf("Please enter the second number:");
rewind(stdin);
scanf("%d", &high);
} while (high < 2 * low);
printf("The odd numbers between %d and %d are: ", low, high);
for (odds = low;odds <= high;odds++) {
if (odds % 2 != 0)
{
printf(" %d", odds);
}
}
printf(".\n");
system("pause"); }
I enter the input which '1' for 'low' variable while '10' for 'high' variable then it shows the result: "The odd numbers between 1 and 10 are 1 3 5 7 9. ".So, how can I improve or change my code by printing output:"The odd ..... 1,3,5,7,9."?
To add commas
int first = 1;
for (odds = low;odds <= high;odds++) {
if (odds % 2 != 0)
{
if(first){ // to prevent comma before first number
first = 0;
} else {
printf("%s",",");
}
printf(" %d", odds);
}
}
could have been
printf("%c", ',');
. Ie a single character, but I used %s just in case you want to add more padding
One nice thing about odd numbers is that you know exactly where they are. Rather that iterating over all the values and checking if each is odd, just find the first odd value and increment by 2:
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char **argv)
{
int low = argc > 1 ? strtol(argv[1], NULL, 10) : 1;
int high = argc > 2 ? strtol(argv[2], NULL, 10) : 10;
printf("The odd numbers between %d and %d are: ", low, high);
if( low % 2 == 0 ){
low += 1;
}
for( int odd = low; odd <= high; odd += 2 ){
printf("%s%d", odd == low ? "" : ", ", odd);
}
putchar('.');
putchar('\n');
return 0;
}
Related
I wrote up a piece of code to find whether a number is prime or not and here it is.
#include <stdio.h>
void main() {
int i, n;
printf("Enter value for n: ");
scanf("%d", &n);
if (n <= 3) {
printf("It is a prime number");
}
for (i = 2; i < n; i++) {
if (n % i == 0) {
printf("It's not prime number \n");
break;
} else {
printf("It is a prime number \n");
break;
}
}
}
However, when my input is 33, instead of the output printing It's not a prime number, since 33 is divisible by 3 and 11, it prints that It is a prime number.
What is the problem with my code here?
In your code, the first time the for loop is executed it immediately triggers either the if condition or else, then breaks, reaches the end and returns. The loop runs a total of 1 iteration max. Change to the following:
for (i = 2; i <= n / i; i++){
if (n % i == 0){
printf("It's not prime number \n");
return 0;
}
}
printf("It is a prime number \n");
Here the for runs correctly. It checks for all dividends, only then it's over and prints the false condition. Note you can optimize your code and only check up to the square root of n, because after that it can't hit true.
And add a return statement here, because the program is already over and doesn't need to continue:
if (n <= 1){
printf("It's not a prime number");
return 0;
}
if (n <= 3){
printf("It is a prime number");
return 0;
}
This also screens off 0, 1, and negative integers which are not prime numbers.
You almost got it right: you just have to make sure the program exits after having established whether a number is prime.
Also, you can stop the loop at n/i.
Last, but not least: main should return a int.
#include <stdio.h>
int main(void){
int i,n;
printf("Enter value for n: \n");
scanf("%d", &n);
if (n <= 3){
printf("It is a prime number\n");
return 0;
}
for (i = 2; i < n/i; i++){
if (n % i == 0){
printf("It's not prime number \n");
return 0;
}
}
printf("It is a prime number \n");
return 0;
}
There are multiple problems:
void main() should be int main()
you should check the return value of scanf and reject negative numbers
0 and 1 are not considered prime numbers.
you should end the program if the number matches the first test.
you output the result after a single test: it is correct if the test if (n % i == 0) is true as you have found a divisor, but if you have not, you should iterate, testing all possible divisors up to and including floor(sqrt(n)).
Here is a modified version:
#include <stdio.h>
int main() {
int i, n;
printf("Enter value for n: ");
if (scanf("%d", &n) != 1) {
printf("input error, not a number\n");
return 1;
}
if (n < 0) {
printf("number should be positive: %d\n", n);
return 1;
}
if (n <= 1) {
printf("%d is not a prime number\n", n);
return 0;
}
for (i = 2; i < n / i; i++) {
if (n % i == 0) {
printf("%d not prime number (divisible by %d)\n", n, i);
return 0;
}
}
printf("%d is a prime number\n", n);
return 0;
}
You might want to try this:
#include <bits/stdc++.h>
int main(){
int i,n;
printf("Enter value for n: ");
scanf("%d", &n);
if (n <= 1){
printf("It is a prime number");
}
for (i = 2; i <= sqrt(n); i++){
if (n % i == 0){
printf("It's not prime number \n");
return 0;
}
}
printf("A prime Number");
return 0;
}
This is happening because in your code for i = 3 and n = 33, if condition is failing which leads to else block directly and hence you are getting output as "It is a prime number".
I have started learning C language. I wrote this program to find all prime numbers between the given range but I am unable to get the expected output.
Can anyone tell me what's wrong with this program please?
#include <stdio.h>
#include <conio.h>
void main() {
int min, max, i, j, count = 0;
printf("Enter Your First Number\n");
scanf("%d", &min);
printf("Enter Your Last Number\n");
scanf("%d", &max);
for(i=min; i<=max; i++) {
for(j=1; j<=i; j++) {
if(i % j == 0) {
count++;
}
}
if(count==2) {
printf("%d\t",i);
}
}
getch();
}
I just suggest getting rid of that count variable.
How do you know if a number N is prime? If for every j in the range (2 to N-1) you have N%j != 0.
So:
In the inner loop, use j from 2 to N-1 (instead of from 1 to N as you used tio do). In fact N%1 and N%N will be 0
The first time you find a j so that N % j == 0 break. You are sure it's not prime
Why incrementing count? For a prime number the j counter will be equal to i (because you looped until j<i, and the last j++ made j
equal to i). So just check for j == i and print the prime number i
#include <stdio.h>
#include <conio.h>
int main( void )
{
int min, max, i, j, count = 0;
printf("Enter Your First Number\n");
scanf("%d", &min);
printf("Enter Your Last Number\n");
scanf("%d", &max);
for(i=min; i<=max; i++)
{
// Was for(j=1; j<=i; j++)
for(j=2; j<i; j++)
{
if(i % j == 0)
{
//Was count++;
break;
}
}
//Was if(count==2)
if(j == i)
{
printf("%d\t",i);
}
}
getch();
return 0;
}
Here you are.
#include <stdio.h>
int main( void )
{
printf( "Enter the range of numbers (two unsigned integer numbers): " );
unsigned int first = 0, last = 0;
scanf( "%u %u", &first, &last );
if ( last < first )
{
unsigned int tmp = first;
first = last;
last = tmp;
}
do
{
int prime = first % 2 == 0 ? first == 2 : first != 1;
for ( unsigned int i = 3; prime && i <= first / i; i += 2 )
{
prime = first % i != 0;
}
if ( prime ) printf( "%u ", first );
} while ( first++ != last );
putchar( '\n' );
return 0;
}
The program output might look like
Enter the range of numbers (two unsigned integer numbers): 0 100
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97
As for your program then you need re-initialize the variable count before the inner loop
for(i=min; i<=max; i++) {
count = 0;
for(j=1; j<=i; j++) {
if(i % j == 0) {
count++;
}
}
And the inner loop is inefficient.
Need to reset the value of count. It starts at count=0, then for any inputs, the loops will count up. The For each outer loop index, it will go like this:
1 (1%1=0 --> count++, count = 1)
2 (2%1=0 --> count++, and 2%2=0 --> count++, count = 3)
3 (3%1=0 --> count++, and 3%3=0 --> count++, count = 5)
etc... until max is reached.
You can use a simple isprime function to check whether a number is prime or not and then call the function for the given interval.
To find whether a number is prime or not , we can use a simple primality test to check it.
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
bool isprime(int n)
{
if(n <= 1) return false;
if(n <= 3) return true;
if(n%2 == 0 || n%3 == 0) return false;
for(int i = 5;i*i <= n;i += 6)
{
if(n%i == 0 || n%(i + 2) == 0)
{
return false;
}
}
return true;
}
int main()
{
int a,b;
printf("Enter the first number :");
scanf("%d",&a);
printf("Enter the second number :");
scanf("%d",&b);
for(int i = a;i <= b;i++)
{
if(isprime(i)) printf("%d ",i);
}
return 0;
}
There is a simple change you should do:
#include <stdio.h>
#include <conio.h>
void main() {
int min, max, i, j, count;
printf("Enter Your First Number\n");
scanf("%d", &min);
printf("Enter Your Last Number\n");
scanf("%d", &max);
for(i=min; i<=max; i++)
{
count=1;
for(j=2; j<=i; j++)
{
if(i % j == 0) {
count++;
}
}
if(count==2) {
printf("%d\t",i);
}
}
}
My answer may be a bit late, but since it's the same issue, i'll write it here in case it helps someone else coming to this thread in the future.
My code is written from the POV of a beginner (No complex functions or data types are used) as this is a code that mostly they will get stuck on.
Working:
User inputs the range.
Using the for loop, each number in the range is sent to the isprime function which returns TRUE or FALSE after checking the condition for being a prime number.
if TRUE : program prints the number.
if FALSE : program skips the number using continue function.
#include<stdio.h>
int isprime(int num);
int main() {
int min, max;
printf("Input the low number: ");
scanf("%d", &min);
printf("Input the high number: ");
scanf("%d", &max);
for(int i = min; i<=max; i++) {
if(isprime(i) == 1) {
printf("%d ", i);
}
else if(isprime(i) == 0){
continue;
}
}
return 0;
}
int isprime(int num) {
int count = 0;
for(int i=2; i<=(num/2); i++) {
if(num % i == 0 ) {
count ++;
}
else{
continue;
}
}
if(count>0){
return 0;
}
else if (count == 0){
return 1;
}
}
Make a program that asks the user for an integer and says if the
number is prime or not. A number greater than 1 is prime if only
is divisible by 1 and by itself. Then, it will tell us what the prime number is.
example:
Enter a number: 8
8 is not first. The first one immediately superior to 8 is 11.
Enter a number: 5
5 is first. The first one immediately above 5 is 7.
I can only solve first part.
Here is my code:
#include <stdio.h>
int main() {
int num, i;
do {
printf("Enter a numer: ");
scanf("%d", & num);
}
while (num < 1);
for (i = 2; i < num; i++) {
if (num % i == 0)
printf("Its prime");
}
if (num % 1 == 0 && num % num == 0)
printf("Not prime");
return 0;
}
Try this logic. Not tested
#include <stdio.h>
int main()
{
int num, i, flag = 0;
printf("Enter a positive integer: ");
scanf("%d", &num);
int isPrime=IsPrime(num)
if(isPrime==0){
numNext=num+1;
int nextPrimeNum=checkNextPrime(numNext);
}
}
int IsPrime(int num){
for(i = 2; i <= num/2; ++i)
{
// condition for nonprime number
if(num%i == 0)
{
flag = 1;
break;
}
}
if (num == 1)
{
flag=1;//neither prime nor composite
}
return flag;
}
int checkNextPrime(int numNext){
int isNextPrime=IsPrime(numNext)
if(isNextPrime==0){
printf("This is the required output :"numNext);
return numNext;
}
else{
numNext=numNext+1;
checkNextPrime(int numNext)
}
}
My assignment is to find all possible modes for a set of numbers (0 to 100).
We were told to do so using arrays and also to count the frequency that each number occurs.
I've coded for the mode, however, my program does not work is there are multiple modes (example: 1, 2, 7, 7, 9, 10, 7, 2, 2. In this stance, 2 and 7 are both the mode and my program needs to print both of them, but mine doesn't).
I think I might have to make another array set, but I'm not sure? Any advice would be appreciated.
Here is what I have:
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
int main() {
int x, i, c[101], mode;
printf("please enter test scores between 0 and 100\n");
i = 0;
mode = 0;
while (i <= 100) { //setting all values to 0
c[i] = 0;
i = i + 1;
}
scanf("%d", &x); // scanning in the test scores
while ((x >= 0) && (x <= 100)) { // counting how often each score appears
c[x] = c[x] + 1;
if (c[x] >= mode) {
mode = x;
}
scanf("%d", &x);
}
printf("THE MODE(S) ARE %d\n", mode);
i = 0;
while (i <= 100) { //printing all values so long as they've occurred at least once
if (c[i] > 0) {
printf("%d occurs %d times\n", i, c[i]);
}
i = i + 1;
}
}
You have to count the highest frequency of any number and if that frequency equals the frequency of any other number then that number will also be mode.
So the changes that you need to do are:
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
int main ()
{
int x, i, c[101], mode;
printf("please enter test scores between 0 and 100\n");
i = 0;
mode = 0;
while (i <= 100) //setting all values to 0
{
c[i] = 0;
++i;
}
scanf("%d", &x); // scanning in the test scores
while ((x >= 0) && (x <= 100)) // counting how often each score appears
{
c[x] = c[x] + 1;
if (c[x] >= mode)
{mode = c[x];}
scanf("%d", &x);
}
for(i=0;i<=100;i++){//printing all values having highest frequency
if (c[i]==mode)
{
printf("THE MODE(S) ARE %d\n", i);
}
i = 0;
while (i<=100) //printing all values so long as they've occurred at least once
{
if (c[i] > 0)
{
printf("%d occurs %d times\n", i, c[i]);
}
++i;
}
}
Instead of determining the mode in the main entry loop, you should determine the maximum count. Then you can print all values with this count of occurrences in a final loop.
You should also check the return values of scanf().
I would also advise to use an initializer for the array to avoid a loop and to use for loops that more clearly identify the initialization, test and increment of the loop index.
Here is a corrected version of your code:
#include <stdio.h>
int main() {
int x, i, c[101] = { 0 }, max_repeat;
printf("please enter test scores between 0 and 100\n");
max_repeat = 0;
// read the test scores and compute the maximum repeat count
while (scanf("%d", &x) == 1 && x >= 0 && x <= 100) {
c[x] += 1;
if (max_repeat < c[x]) {
max_repeat = c[x];
}
}
printf("The mode(s) are");
for (i = 0; i <= 100; i++) {
if (c[i] == max_repeat) {
printf(" %d", i);
}
}
printf("\n");
return 0;
}
Well I have been assigned to do the prime factorisation for composite numbers, but the problem is I have hard-coded it till prime numbers:2,3,5,7,11,13,19 and I want to make it general.
#include <stdio.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
void prime(int flag,int num);
int main()
{
int num, flag, i, div;
printf("Enter your number: ");
scanf("%d", &num);
flag = 1;
prime(flag, num);
printf("Press any key to exit.");
getchar();
return 0;
}
void prime(int flag, int num)
{
void factor(int num, int i);
int sq, i, square;
sq = abs(sqrt(num));
if (num == 2)
flag = 1;
else
for (i = 2; i <= sq; i++)
{
if (num % i == 0)
{
flag = 0;
break;
}
else
flag = 1;
}
if (flag == 1)
printf("\n%d is a prime number", num);
else
{
printf("\n%d is not a prime number\n", num);
factor(num, i);
}
}
void factor(int num, int i)
{
for (i = 2; i <= num; i++)
{
again:
if(num % i == 0)
{
num = num / i;
printf("%d x", i);
if (num != (2||3||5||7||11||17||19))
goto again;
}
}
printf("1\n\n");
}
P.S.:Try to make it as simpler as possible.
The problem is after dividing it with smallest prime. i.e. 2 the next step should be check the number whether it is a prime or not. If not, then factorise it but I dont know how to do it.
Plz help.
Thx in advance.
#include <stdio.h>
void factor(int num);
int main(void){
int num;
printf("Enter positive number(more than 1): ");
if(1 != scanf("%d", &num) || num < 2){
printf("invalid input!\n");
return -1;
}
scanf("%*[^\n]");scanf("%*c");//clear upto line end
factor(num);
printf("Press any key to exit...");
getchar();
return 0;
}
void factor(int num){
int i, flag = 0;
if(num == 2){
printf("\n%d is a prime number\n", num);
return ;
}
while(!(num & 1)){
if(!flag)
printf("\n%d is not a prime number\n", num);
flag = 1;
printf("2 x ");
num >>= 1;
}
for (i = 3; i*i <= num; i += 2){
while(num % i == 0){
if(!flag)
printf("\n%d is not a prime number\n", num);
flag = 1;
printf("%d x ", i);
num /= i;
}
}
if(!flag)
printf("\n%d is a prime number\n", num);
else if(num != 1)
printf("%d x 1\n\n", num);
else
printf("1\n\n");
}
Replace line,
if (num!=2&& num!=3 && num!=5 && num!=7 && num!=11 && num!=17 && num!=19)
instead of,
if (num!=2||3||5||7||11||17||19)
In function factor, first try dividing by 2 repeatedly, then try every odd number while said odd number squared is less or equal to num. This simple method is a bit redundant as you try and divide by composite numbers, but since you will already have removed all smaller prime factors, num will not be divisible by such composite numbers. Iterating while i * i <= num will stop much earlier than with your current i <= num test.
Try and write code to implement the above algorithm and post it as an edit.