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I'm just starting to learn C. I wrote this beautiful little program that was meant to print "11111". But the pow function doesn't actualize the variable, that changes every time, that is being used in it.
I created the loop using if, goto and adding 1's. That's the only way I know to create a loop yet.
Can I overcome this problem using the same tools I've used?
Here's my code:
#include <stdio.h>
#include <math.h>
main (void)
{
int b = 0;
int a = 0;
int c = 0;
up:
b = pow (10,a);
c = c + b;
a = a + 1;
if (a = 6)
{
goto stop;
}
else
{
goto up;
}
stop:
printf("%d\n",c);
}
if (a = 6)
That sets a to 6.
You probably meant:
if (a == 6)
Related
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why doesn't this program print anything?
int main(){
int a = getchar()-'0';
getchar();
int b = getchar()-'0';
int vsota = 0;
vs = (a+b)%10;
putchar(vs);
printf("\n");
}
I put in the numbers 7 and 9 and it was supossed to outprint 6 but it does not.
putchar(vs); writes the character whose code is the value in vs. The value in vs is 6. So it writes the character with code 6. That character is not the digit “6”. You do not see anything because it is a “control character” with no visible appearance. To write the character for the digit whose value is in vs, use putchar('0' + vs);.
Also, fix this:
int vsota = 0;
vs = (a+b)%10;
That would not have compiled, so presumably you made a mistake when entering code into Stack Overflow. Use the same name in both places.
because you try to output non printable character
int main(){
int a = '1'-'0';
int b = '6'-'0';
int vsota = 0;
vsota = (a+b)%10;
putchar(vsota + '0');
printf("\n");
}
https://godbolt.org/z/NAyrNn
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#include <stdio.h>
#include <stdlib.h>
#define size 20000000
int prim[size];
int i, zahl, zaehler, erg;
int sieve(int zahl, int prim[], int zaehler) {
if(zahl == 2000000)
return 1;
for(i=0; i<=zaehler; i++) {
erg = zahl%prim[i];
if(erg==0) {
zahl++;
return sieve(zahl, prim, zaehler);
}
}
zaehler++;
prim[zaehler]=zahl;
zahl++;
printf("%d\n", prim[zaehler]);
return sieve(zahl, prim, zaehler);
}
int main(){
zaehler = 0;
zahl = 2;
for(i=0;i<size;i++)
prim[i]=2;
sieve(zahl, prim, zaehler);
}
When trying to calculate prime numbers, when i run this code, it always crushes at the number 64901.
What might be the problem?
Ironically, this is literally a stack overflow due to recursion. You can make your stack large (which will only delay the issue), or change from a recursive solution to an iterative one.
(and for what it's worth, some debuggers won't be able to help you in this situation. And it's very difficult to beginners in C to understand what is going wrong until the first time they hit this problem. So congrats! You're leveling up in C)
A cheap way to verify it's indeed a stack overflow is to create extra memory on your stack in the recursive function and see if the number it crashes on changes from 64901. My guess is if you put like char dummy[2048] in there, it will crash much sooner.
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Below is a C program which wants to multiply an integer by 5 using bitwise operation. But when i run this program it gives unexpected output. I know there is something i messing up which i could not see. Any help regarding this guys and girls ?
#include <stdio.h>
#define PrintInt(expr) printf("%s : %d\n",#expr,(expr))
int FiveTimes(int a)
{
int t;
t = a<<2 + a;
return t;
}
int main()
{
int a = 1, b = 2,c = 3;
PrintInt(FiveTimes(a));
PrintInt(FiveTimes(b));
PrintInt(FiveTimes(c));
return 0;
}
This is a question of "operator precedence": "<<" has a lower priority than "+" - so your code actually calculates a << (2 + a), while it should be (a << 2) + a. The latter is the fix.
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i cant get the following code to run, ie it dosent give out any output
the objective is to find the sum of all primes below 2 million,
#include <stdio.h>
#include <math.h>
int is_prime(long long int i)
{
long long int n;
if(i==2)
return 1;
for(n=2;n<=sqrt(i);n++)
if(i%n==0)
return 0;
return 1;
}
int main()
{
long long int s=0,i=2;
for(i<2000000;i++;)
{
if(is_prime(i))
s=s+i;
}
printf("sum: %lli",s);
return 0;
}
You're using the for loop wrong. A for loop looks like this:
for(initialization; test expression; update)
But you wrote
for(i<2000000;i++;)
which should be
for(;i<2000000;i++)
ie, skip initialization, on each iteration test for i<2000000 and increment.
Your problem is that you are essentially factorising every integer up to two million for this. It's not that your code isn't working, it just is running very very slowly. If you attach a debugger to it you will most likely be at line
if(i%n==0)
most of the time.
Implement the Sieve of Eratostenes. Will be the most effective here.
Also your loop for(i<2000000;i++;) will run for 2^64 cycles.
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This is related to the "Project Euler Problem 14"
As I think, my logic and the code is good enough,but it may take few seconds to give the answer.
But when i run this code, the program stops when "starting_number" is around 103152(i can't remember the number exactly).
Can anybody please have a look at this code and, tell me where and what's wrong with this code.
Here's the code :
#include<stdio.h>
int starting_number;
int number_of_terms;
int j=0,k=0;
int term;
int main(){
for(starting_number=2;starting_number<1000000;starting_number++){
term = starting_number;
number_of_terms = 1;
while(1){
{
if(term%2==0){
term = term/2;
number_of_terms++;
} else if(term%2!=0){
term = 3*term + 1;
number_of_terms++;
}
}
if(term == 1) break;
}
if(j>=number_of_terms) //finding which chain is longer
j=j;
else if(j< number_of_terms) {
j= number_of_terms;
k=starting_number;
}
printf("\n%d",starting_number);
}
printf("\n%d(%d)\n",k,j);
return 0;
}
This one's mildly tricky, but your problem is here:
if(term == 1) break;
If the variable term becomes very large (as it can easily do) then it can overflow the int datatype.
When this happens term becomes negative. The C language modulus of a negative odd number is itself negative. Therefore, the end condition for your loop is never met.
Solve this problem by using a larger data type such as unsigned long long.
A less convoluted version of your code would appear as follows. Note that I have eliminated the global variables (those outside of your main function) because global variables are evil. I've replaced your infinite while-loop with a loop that uses an end condition. I've reduced duplication of code within the while-loop. I've eliminated the j=j case. Since printf is a slow function to run, I've commented out the prinft you had in the for loop, which improves the run-time significantly.
#include <stdio.h>
int main(){
int number_of_terms;
unsigned long long term;
int j=0,k=0;
for(int starting_number=2;starting_number<1000000;++starting_number){
term = starting_number;
number_of_terms = 1;
while(term!=1){
if(term%2==0)
term /= 2;
else
term = 3*term + 1;
number_of_terms++;
}
if(j<number_of_terms){ //finding which chain is longer
j = number_of_terms;
k = starting_number;
}
//printf("\n%d",starting_number);
}
printf("\n%d(%d)\n",k,j);
return 0;
}
And, indeed, using unsigned long long solves the problem.