long long output in c++

Question

#include<iostream>

using namespace std;

long long num;
long long dp[90];


int solve(int a)
{
dp[0]=1;
dp[1]=1;
for(int i = 2; i<a; i++)
{
    dp[i] = dp[i-1] + dp[i-2];
}
return dp[a-1];
}
int main()
 {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);

 cin >> num;
 solve(num);
 cout << dp[num-1];//problem.

 return 0;
 }

because dp size is oversize in int, so i use long long type.

when i using to "cout<< solve(num)", i input value to 47; as a result, i got error(-291928302)

when i use above code("cout << dp[num-1]"), i got normal value.

what are two different?

Answer 1

solve()'s return type is int rather than long long.