Error in a code and cant find out why

[Nata]

I should write a function which will count how many words are in a sentence. I thought that this should be right however, there is some error and I do not get why. Could you please help me?

#include <iostream>
#include <string>
using namespace std;
void f1(string);
int main()
{

    string a;
    getline(cin,a);
    f1(a);

}


void f1(string a){

    int count=0;
    if(a==' '){
        
        count++;
        
    }
    

}

[Nata]

Error is on line 18. Please help.

[Nata]

okay I already got it if anyone needs help with this kind of thing in the future here is the code:

#include <iostream>
#include <string>
using namespace std;
void f1(string a);
int main()
{
    
    string a;
    getline(cin,a);
    f1(a);
    
}


void f1(string a){
    
    int count=1;
    for (int i=0;i<a.length();i++){
        if(a[i]==' '){
            
            count++;
            
        }
        
    }
    cout<<count;
    
}