Getting the warning: ' In function ‘void dfs(int)’ Warning: comparison between signed and unsigned integer expressions'

Question

I am working on a simple DFS problem where I have to return the number of respective child nodes having more child nodes as compared to their parents (Child nodes>Parent nodes:Count++).

I have been facing the problem I mentioned in the title and I haven't been able to work around it. I used unsigned int too, but to no avail. I am clear with my logic for this question, but fairly new to coding and hence face difficulties with errors such as this. I will attach only my DFS function below, where the problem seems to be occurring. Please help me with this. (Using adjacency list)

vector<int> adj[100001];
bool visited[100001]={false};
int parent=0;
int child=INT_MAX;
int counterr=0;

/*Recursive DFS:*/

void dfs(int s){
    child=adj[s].size()-1;
    if(child>parent)
        counterr++;
    if(s==1)
        parent=adj[s].size();
    else
        parent=adj[s].size()-1;
    visited[s]=true;
    for(int i=0;i<adj[s].size();i++)
    {
        if(visited[adj[s][i]==false])
            dfs(adj[s][i]);
    }
}

Answer 1

For the most part, you can ignore this. However, if your integer exceeds the normal integer limit, or your adj[s] vector is empty, this may become a problem. If parent is never negative you can just change the line

int parent;

to

unsigned int parent;

which will completely prevent this warning.

Answer 2

for(int i=0;i<adj[s].size();i++)

You get this warning because adj[s].size() is unsigned integer, but i is signed.

For fix that warning use this instead, and i became unsigned.

for (size_t i=0; i < adj[s].size(); i++)