c++ nested loop output result

Question

I want to output this result at screen :

1
23
456
78910

how to do that??
I tried to write this code:

for (int line = 1; line <= 4; line++){
    int num = line;
    int i = 1;
    for (int x = 1; x <= line; x++){
        cout << num;
        num = num + i;
    }
    cout << endl;
}

but the output is :

1
23
345
4567

please help !!!

Answer 1

Create num outside the for loop and increment it after you write it out.

int num = 1;
for (int line = 1; line <= 4; line++){
    for (int x = 1; x <= line; x++){
        cout << num;
        ++num;
    }
    cout << endl;
}

Answer 2

int num = 1;
int i = 1;
for (int line = 1; line <= 4; line++){
    for (int x = 1; x <= line; x++){
        cout << num;
        num = num + i;
    }
    cout << endl;
}