Simple program does not compile [closed] - c++

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Closed 11 years ago.
I am using Dev-C++. It doesn't show any code error, but fails to work.
It works when I try small numbers like 10 or 20
I am working on this problem :
Each new term in the Fibonacci sequence is generated by adding the
previous two terms. By starting with 1 and 2, the first 10 terms will
be:
1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
By considering the terms in the Fibonacci sequence whose values do not
exceed four million, find the sum of the even-valued terms.
#include<stdio.h>
#include<stdlib.h>
int main()
{
const int N=100;
int a=1,b=2,i,t[N],S=0,c,j;
t[0]=1;
t[1]=2;
for(i=2;i<N;i++){
t[i]=t[i-2]+t[i-1];
if(t[i]>4000000)
{
for(j=1;j<=i-1;j++){
c=t[j]%2;
if(c==0){
S=S+t[j];
}
else {
continue;
}}
break;
}
}
printf("%d\n",S);
system("pause");
}

Answer 1

You cannot define a variable size array (T[N]). If you make N const, problem should be solved.
const int N = 3999998;
int T(N);
Also, main should have a return type. Change to "int main()"?

Answer 2

You don't need an array to store all those numbers, you can get away with storing the last two terms in the sequence, since that's all that's need to calculate the next term.
Trying to allocate that much space on the stack is asking for trouble since the stack is a relatively limited resource.
In fact, that exact code entered into gcc on a Linux box gives me a segmentation violation when I try to run it, for precisely that reason.
On top of that, your code is not getting the even valued terms, it's getting every term, and you're getting the first four million values, rather than the values below four million which was specified.
The sort of code you're after would look like this:
#include <stdio.h>
int main (void) {
// Accumulator and terms (acc is zero because first two terms are odd).
int acc = 0, t1 = 1, t2 = 1, t3;
// Continue until next term is 4mil or more.
while ((t3 = t1 + t2) < 4000000) {
// printf ("DEBUG: %d %d %d %s\n", t1, t2, t3,
// ((t3 % 2) == 0) ? "<<" : "");
// Accumulate only even terms.
if ((t3 % 2) == 0) acc += t3;
// Cycle through terms.
t1 = t2; t2 = t3;
}
// Print the accumulated value.
printf ("%d\n", acc);
return 0;
}
And the output:
4613732
If you test that program by un-commenting the debug statement, you see:
DEBUG: 1 1 2 <<
DEBUG: 1 2 3
DEBUG: 2 3 5
DEBUG: 3 5 8 <<
DEBUG: 5 8 13
DEBUG: 8 13 21
DEBUG: 13 21 34 <<
DEBUG: 21 34 55
DEBUG: 34 55 89
DEBUG: 55 89 144 <<
DEBUG: 89 144 233
DEBUG: 144 233 377
DEBUG: 233 377 610 <<
DEBUG: 377 610 987
DEBUG: 610 987 1597
DEBUG: 987 1597 2584 <<
DEBUG: 1597 2584 4181
DEBUG: 2584 4181 6765
DEBUG: 4181 6765 10946 <<
DEBUG: 6765 10946 17711
DEBUG: 10946 17711 28657
DEBUG: 17711 28657 46368 <<
DEBUG: 28657 46368 75025
DEBUG: 46368 75025 121393
DEBUG: 75025 121393 196418 <<
DEBUG: 121393 196418 317811
DEBUG: 196418 317811 514229
DEBUG: 317811 514229 832040 <<
DEBUG: 514229 832040 1346269
DEBUG: 832040 1346269 2178309
DEBUG: 1346269 2178309 3524578 <<
4613732
and, if you add up all the even numbers at the end of those DEBUG lines, you do indeed get the given value.

Answer 3

Two things I notice are that main doesn't have a return type (try int main()) and N is used as an array size but isn't constant.

Answer 4

It's a very common programming error called "Stack overflow". In fact, it's so common that it has named a very popular question and answer site, "Stack Overflow", maybe you have heard about it?
(I've been waiting for being able to give this answer ever since I joined "Stack Overflow"!!!)