Write a program to read m and n from keyboard and list all possible combinations to get the score m-n : i am new on stack overflow

This task is from my lab assignment and i am lost i cant find algorithm please help me out .
Thanks

Consider the final score of a football match is m-n where m and n are non-negative integers.
Write a c++ program to read m and n from keyboard and list all possible combinations to get the score m-n.

Example outputs: 

input m : 1
input n : 0
Possible combinations:
0-0, 1-0

input m : 4
input n : 0
Possible combinations:
0-0, 1-0, 2-0, 3-0, 4-0


input m : 1
input n : 1
Possible combinations:
0-0, 1-0, 1-1
0-0, 0-1, 1-1


input m : 2
input n : 1
Possible combinations:
0-0, 1-0, 2-0, 2-1
0-0, 1-0, 1-1, 2-1
0-0, 0-1, 1-1, 2-1

input m : 2
input n : 2
Possible combinations:
0-0, 1-0, 1-1, 2-1, 2-2
0-0, 1-0, 1-1, 1-2, 2-2
0-0, 1-0, 2-0, 2-1, 2-2
0-0, 0-1, 1-1, 1-2, 2-2
0-0, 0-1, 1-1, 2-1, 2-2
0-0, 0-1, 0-2, 1-2, 2-2



this is the code that i have tried when user enters m=2 and n=1 this code prints only two combinations like
 0-0, 1-0, 2-0, 2-1
 0-0, 0-1, 1-1, 2-1
    
    
    {
    int m, n;
    cout<<"Enter the finals scores of both teams";
    cout<<"\nenter the score for team m :";
    cin>>m;
    cout<<"Enter the score for team n :";
    cin>>n;
    if	(m < 0 && n < 0){
               
			cout<<"score can't be negative";
        	cout<<"\nenter the score for team m :";
        	cin>>m;
        	cout<<"Enter the score for team n :";
        	cin>>n;
   		}
    else{
            int k=0;
            if (n==0){
			    for (int j = 0; j <= m; j++){
                    for (k; k <= n; k+=1){
                    	
                        cout<<j<<"-"<<k<<",\t";
                    }
                    k--;
                }
            }
            else if(m==1 && n==1){
                
				int i=0;
                int k=0;
				for (int j = 0; j <= m; j++){
                    for (k; k <= n; k+=1){
                    	
                        cout<<j<<"-"<<k<<",\t";
                    }
                    k--;
                }
                cout<<endl<<endl;
				for (int j = 0; j <= n; j++){
                    
                    for (i; i <= m; i+=1){
                    	
                        cout<<i<<"-"<<j<<",\t";
                    }
                    i--;
                }
            }
            else {
				int i=0;
                int k=0;
				for (int j = 0; j <= m; j++){
                    for (k; k <= n; k+=1){
                    	
                        cout<<j<<"-"<<k<<",\t";
                    }
                    k--;
                }
              
                cout<<endl<<endl;
				for (int j = 0; j <= n; j++){
                    
                    for (i; i <= m; i++){
                    	
                        cout<<i<<"-"<<j<<",\t";
                    }
                    i--;
                }            	
			} 
            
    	}
            
}