Write a program to check a string contain only digit?

Given a string we have to check whether string contain digits only.

Example:

Input:1234
output:true

Input:abcd1
output:false

Logic:

step 1-find a length of string and initialise count variable.
step 2-iterate whole string and if you found number then increment count.
step 3-if count==length then return true

#include<bits/stdc++.h>
using namespace std;
int main()
{
    string s;
    cin>>s;
    int count=0;
    for(int i=0;i<s.length();i++)
    {
        if(isdigit(s[i]))
        {
            count++;
        }
    }
    if(count==s.length())
    {
        cout<<"string contain digit only"<<endl;
    }
    else
    {
                cout<<"string contain not digit only"<<endl;

    }
    
}

Output:

1234
string contain only digit 

Time Complexity-O(N)

Space Complexity-O(1)