I'm trying to solve Problem 4 -Project Euler and I am stucked. So I need a little help with my code. Here is the problem I am trying to solve:
A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.
Find the largest palindrome made from the product of two 3-digit numbers.
Code:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int is_palindrom(int number, int revrse) {
char str1[6];
char str2[6];
sprintf(str1, "%d", number);
sprintf(str2, "%d", revrse);
return strcmp(str1, str2);
}
int main(void) {
int number, revrse;
int i, j, temp;
int maks;
for(i=999;i>99;i--)
for(j=999;j>99;j--) {
temp = number = i*j;
while (temp != 0) {
revrse = revrse * 10;
revrse = revrse + temp%10;
temp = temp/10;
}
if(is_palindrom(number, revrse)==0 && number > maks)
maks = number;
}
printf("%d",maks);
return 0;
}
The revrse var isn't initialized so there are rubbish in it. Remember to always init a variable!
Complementing the answer from #kleszcz, revrse must always be initialized before the while loop begins, otherwise, it will hold the previous value (and rubbish in the first iteration, as he intelligently pointed out).
Another issue is that you do not need the is_palindrome function. You can check directly if the numbers are equal.
To get the reversed form of your number properly, you need to first set an initial value for revrse of 0 for each iteration of your loop, otherwise the behavior is undefined. It also helps to set an initial value for maks to compare against. Finally, why use a function to check for palindromes when you can just check for equality between your number and its reverse?
int main()
{
int number;
int i,j,temp;
int maks = -1;
int revrse;
for(i=999;i>99;i--) {
for(j=999;j>99;j--) {
number = i*j;
revrse = 0;
temp=number;
while (temp != 0){
revrse = revrse * 10;
revrse = revrse + temp%10;
temp = temp/10;
}
if(number == revrse) {
if(number > maks) {
maks = number;
}
}
}
}
printf("%d",maks);
return 0;
}
Related
As a C fresher, I am trying to write a recursive routine to convert a decimal number to the equivalent binary. However, the resultant string is not correct in the output. I think it has to be related to the Type casting from int to char. Not able to find a satisfactory solution. Can anyone help? Thanx in advance.
Code:
#include <stdio.h>
#include <conio.h>
int decimal, counter=0;
char* binary_string = (char*)calloc(65, sizeof(char));
void decimal_to_binary(int);
int main()
{
puts("\nEnter the decimal number : ");
scanf("%d", &decimal);
decimal_to_binary(decimal);
*(binary_string + counter) = '\0';
printf("Counter = %d\n", counter);
puts("The binary equivalent is : ");
puts(binary_string);
return 0;
}
void decimal_to_binary(int number)
{
if (number == 0)
return;
else
{
int temp = number % 2;
decimal_to_binary(number/2);
*(binary_string + counter) = temp;
counter++;
}
}
Should the casting store only the LSB of int in the char array each time?
Do not use global variables if not absolutely necessary. Changing the global variable in the function makes it very not universal.
#include <stdio.h>
char *tobin(char *buff, unsigned num)
{
if(num / 2) buff = tobin(buff, num / 2);
buff[0] = '0' + num % 2;
buff[1] = 0;
return buff + 1;
}
int main(void)
{
char buff[65];
unsigned num = 0xf1;
tobin(buff, num);
printf("%s\n", buff);
}
#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
int decimal, counter=0;
//char* binary_string = (char*)calloc(65, sizeof(char));
//C does not allow initialization of global variables with
//non constant values. Instead declare a static char array with 65 elements.
//Alternatively declare binary_string in the main function and allocate memory with calloc.
char binary_string[65];
void decimal_to_binary(int);
int main()
{
puts("\nEnter the decimal number : ");
scanf("%d", &decimal);
decimal_to_binary(decimal);
//*(binary_string + counter) = '\0';
// This is more readable:
binary_string[counter] = '\0';
printf("Counter = %d\n", counter);
puts("The binary equivalent is : ");
puts(binary_string);
return 0;
}
void decimal_to_binary(int number)
{
if (number == 0)
return;
else
{
int temp = number % 2;
//decimal_to_binary(number/2);
//you call decimal_to_binary again before increasing counter.
//That means every time you call decimal_to_binary, the value of count
//is 0 and you always write to the first character in the string.
//*(binary_string + counter) = temp;
//This is more readable
//binary_string[counter] = temp;
//But you are still setting the character at position counter to the literal value temp, which is either 0 or 1.
//if its 0, you are effectively writing a \0 (null character) which in C represents the end of a string.
//You want the *character* that represents the value of temp.
//in ASCII, the value for the *character* 0 is 0x30 and for 1 it is 0x31.
binary_string[counter] = 0x30 + temp;
counter++;
//Now after writing to the string and incrementing counter, you can call decimal_to_binary again
decimal_to_binary(number/2);
}
}
If you compile this, run the resulting executable and enter 16 as a number, you may expect to get 10000 as output. But you get00001. Why is that?
You are writing the binary digits to the string in the wrong order.
The first binary digit you calculate is the least significant bit, which you write to the first character in the string etc.
To fix that aswell, you can do:
void decimal_to_binary(int number){
if(number == 0){
return;
}
else{
int temp = number % 2;
counter++;
//Store the position of the current digit
int pos = counter;
//Don't write it to the string yet
decimal_to_binary(number/2);
//Now we know how many characters are needed and we can fill the string
//in reverse order. The first digit (where pos = 1) goes to the last character in the string (counter - pos). The second digit (where pos = 2) goes to the second last character in the string etc.
binary_string[counter - pos] = 0x30 + temp;
}
}
This is not the most efficient way, but it is closest to your original solution.
Also note that this breaks for negative numbers (consider decimal = -1, -1 % 2 = -1).
this is my code, I want to make a function that when it is called will generate a number between 1111 to 9999, I don't know how to continue or if I've written this right. Could someone please help me figure this function out. It suppose to be simple.
I had to edit the question in order to clarify some things. This function is needed to get 4 random digits that is understandable from the code. And the other part is that i have to make another function which is a bool. The bool needs to first of get the numbers from the function get_random_4digits and check if there contains a 0 in the number. If that is the case then the other function, lets call it unique_4digit, should disregard of that number that contained a 0 in it and check for a new one to use. I need not help with the function get_random_4digitsbecause it is correct. I need helt constructing a bool that takes get_random_4digits as an argument to check if it contains a 0. My brain can't comprehend how I first do the get_random_4digit then pass the answer to unique_4digits in order to check if the random 4 digits contains a 0 and only make it print the results that doesn't contain a 0.
So I need help with understanding how to check the random 4 digits for the integer 0 and not let it print if it has a 0, and only let the 4 random numbers print when it does not contain a 0.
the code is not suppose to get more complicated than this.
int get_random_4digit(){
int lower = 1000, upper = 9999,answer;
answer = (rand()%(upper-lower)1)+lower;
return answer;
}
bool unique_4digits(answer){
if(answer == 0)
return true;
if(answer < 0)
answer = -answer;
while(answer > 0) {
if(answer % 10 == 0)
return true;
answer /= 10;
}
return false;
}
printf("Random answer %d\n", get_random_4digit());
printf("Random answer %d\n", get_random_4digit());
printf("Random answer %d\n", get_random_4digit());
Instead of testing each generated code for a disqualifying zero just generate a code without zero in it:
int generate_zero_free_code()
{
int n;
int result = 0;
for (n = 0; n < 4; n ++)
result = 10 * result + rand() % 9; // add a digit 0..8
result += 1111; // shift each digit from range 0..8 to 1..9
return result;
}
You can run the number, dividing it by 10 and checking the rest of it by 10:
int a = n // save the original value
while(a%10 != 0){
a = a / 10;
}
And then check the result:
if (a%10 != 0) printf("%d\n", n);
Edit: making it a stand alone function:
bool unique_4digits(int n)
{
while(n%10 != 0){
n = n / 10;
}
return n != 0;
}
Usage: if (unique_4digits(n)) printf("%d\n", n);
To test if the number doesn't contain any zero you can use a function that returns zero if it fails and the number if it passes the test :
bool FourDigitsWithoutZero() {
int n = get_random_4digit();
if (n % 1000 < 100 || n % 100 < 10 || n % 10 == 0) return 0;
else return n;
}
"I need not help with the function get_random_4digits because it is correct."
Actually the following does not compile,
int get_random_4digit(){
int lower = 1000, upper = 9999,answer;
answer = (rand()%(upper-lower)1)+lower;
return answer;
}
The following includes modifications that do compile, but still does not match your stated objectives::
int get_random_4digit(){
srand(clock());
int lower = 1000, upper = 9999,answer;
int range = upper-lower;
answer = lower + rand()%range;
return answer;
}
" I want to make a function that when it is called will generate a number between 1111 to 9999,"
This will do it using a helper function to test for zero:
int main(void)
{
printf( "Random answer %d\n", random_range(1111, 9999));
printf( "Random answer %d\n", random_range(1111, 9999));
printf( "Random answer %d\n", random_range(1111, 9999));
printf( "Random answer %d\n", random_range(1111, 9999));
return 0;
}
Function that does work follows:
int random_range(int min, int max)
{
bool zero = true;
char buf[10] = {0};
int res = 0;
srand(clock());
while(zero)
{
res = min + rand() % (max+1 - min);
sprintf(buf, "%d", res);
zero = if_zero(buf);
}
return res;
}
bool if_zero(const char *num)
{
while(*num)
{
if(*num == '0') return true;
num++;
}
return false;
}
I want to make a program to count the sum of digits in a string but only using stdio.h
but the program needs to count until its less than 10
so the example you input 56 it would be 5+6=11 then 1+1=2 and so on
here's my code. For now I'm just confused how to check if its whether more than 9 or not
#include<stdio.h>
int plus(int n);
int main(void)
{
int n, digit, test;
scanf("%d", &n);
test = plus(n);
while(test != 0)
{
if(test > 9)
plus(test);
else
break;
}
printf("%d", test);
}
int plus(int n)
{
int digit=0,test=0;
while(n != 0)
{
digit = n%10;
test = test + digit;
n = n/10;
}
return test;
}
You are not storing the value returned by plus function in the while body.
You can change the condition in while to check whether it is greater than 9 or not, and assign test as test = plus(test);
So, your while will look like this.
while(test > 9)
{
test=plus(test);
}
You need to recursively call the function plus() until the value returned by it becomes less than 10. Like shown below:
int main(void)
{
int n=56;
while(n> 10)
{
n = plus(n);
}
printf("%d", n);
}
#include<stdio.h>
int main(void)
{
int rev=0,temp=0,frwd,n,ans=0;
int i,j;
for(i=100;i<=999;i++)
{
for(j=i;j<=999;j++)
{
n = i*j;
frwd = n;
while(n!=0)
{
temp = n%10;
n = n/10;
rev = temp+rev*10;
}
printf("%d",rev);
if((rev == frwd)&&(ans<frwd))
{
ans=frwd;
printf("%d",ans);
}
}
}
return(0);
}
I have tried working out everything but this code doesn't seem to give the correct output.
The desired output is largest palindrome number of 6 digits.
If I am running the individual parts i.e. the reversing of number , checking of number whether or not it is a palindrome or the for loops, they are working fine but in the program they are giving garbage as output.
Any help would be appreciated.
ya the problem is that you are not reinitializing rev to 0 as said by cowanother.anon.ard. Try putting rev=0 in inner for loop.
But you cant get 999999 as the highest palindrome number of 6 digit by your method as u r not checking all the 6 digit numbers.
#include<stdio.h>
int main(void)
{
int rev=0,temp=0,frwd,n,ans=0;
int i,j;
for(i=100000;i<=999999;i++)
{
frwd = n = i;
rev = 0;
while(n!=0)
{
temp = n%10;
n = n/10;
rev = temp+rev*10;
}
if((rev == frwd)&&(ans<frwd))
{
ans=frwd;
}
}
printf("%d\n",ans);
return(0);
}
4 problems with your Code:-
Like another.anon.coward said- you need to put rev=0 inside inner loop
You need to separate each number printed either by a space or a newline ('\n')
printf("\n %d");. Otherwise they will look like one big number (garbage).
Your algorithm is also wrong. According to your program, the largest 6-digit number is 906609 (The correct answer is 999999). For this you should change your inner loop to j=0;j<999;j++ and change n=i*j to n=i*1000+j.
Also move the printf("\n%d",ans); outside the loop.
The corrected program is:
#include <stdio.h>
int main(void)
{
int rev=0,temp=0,frwd,n,ans=0;
int i,j;
for(i=100;i<=999;i++)
{
for(j=0;j<=999;j++) /*CORRECTED THIS LINE,*/
{ rev=0;/*ADDED THIS LINE;*/
n = (i*1000) + j; /*CORRECTED THIS LINE*/
frwd = n;
while(n!=0)
{
temp = n%10;
n = n/10;
rev = temp+rev*10;
}
printf("\n%d",rev); /*THIS LINE,*/
if((rev == frwd)&&(ans<frwd))
{
ans=frwd;
}
}
}
printf("\n%d",ans); /* AND THIS LINE*/
return(0);
}
#include <stdio.h>
int main(void)
{
int rev=0,temp=0,frwd,n,ans=0;
int i,j;
for(i=100;i<=999;i++)
{
for(j=0;j<=999;j++) /*CORRECTED THIS LINE,*/
{ rev=0;/*ADDED THIS LINE;*/
n = (i*1000) + j; /*CORRECTED THIS LINE*/
frwd = n;
while(n!=0)
{
temp = n%10;
n = n/10;
rev = temp+rev*10;
}
printf("\n%d",rev); /*THIS LINE,*/
if((rev == frwd)&&(ans<frwd))
{
ans=frwd;
}
}
}
printf("\n%d",ans); /* AND THIS LINE*/
return(0);
}
I've written some code in C to try adn find whether or not a number is a Palindrome. The rule is that two 3 digit numbers have to be multiplied together and you have to find the highest palindrome. the answer should be 906609 but my code only gets to 580085.
the code:
#include <stdio.h>
#include <stdlib.h>
/* Intialise */
void CalcPalin();
int CheckPalin(int number);
/* Functions */
void CalcPalin()
{
int result = 0;
int palin = 0;
int FNumber = 0;
int FNumber2 = 0;
int number = 99;
int number2 = 100;
while(number2 < 1000)
{
number += 1;
/*times together - calc result*/
result = number * number2;
if(CheckPalin(result) == 1)
{
palin = result;
FNumber = number;
FNumber2 = number2;
}
if(number == 999)
{
number = 99;
number2 += 1;
}
}
printf(" Result = %d, by Multiplying [%d] and [%d]", palin, FNumber, FNumber2 );
}
int CheckPalin(int number)
{
int checknum, checknum2 = 0;
checknum = number;
while(checknum)
{
checknum2 = checknum2 * 10 + checknum % 10;
checknum /= 10;
}
if( number == checknum2)
return 1;
else
return 0;
}
int main( void)
{
CalcPalin();
return EXIT_SUCCESS;
}
Im pretty sure its a stupid answer and im over looking something simple but i cant seem to find it. Any help would be great
You have not tested whether the current result is higher than one old result. Add this check.
// test new result is higher than old palin before setting this as palin
if(CheckPalin(result) == 1 && palin < result)
Your algorithm print :
Result = 580085, by Multiplying [583] and [995]
It seems that you should find a way to increment more the 1st number. There is many possibility between 583 and 999 in order to get to 906609.
EDIT : In fact, you are looking for 993 * 913 = 906609.