Problem with either rand() or loops....not sure

This is a discussion on Problem with either rand() or loops....not sure within the C++ Programming forums, part of the General Programming Boards category; My aim is to print out a grid of random characters, either a G, a W or an A. Here ...

  1. #1
    Let's do some coding! Welshy's Avatar
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    Problem with either rand() or loops....not sure

    My aim is to print out a grid of random characters, either a G, a W or an A. Here is my code (obviously with int main() etc):

    Code:
        srand(time(0));
        
        char terrain[5][5];
        
        for (int i = 0;i < 5; i++)
        {
            for (int j = 0;j < 5; j++)
            {
                int temp = (rand() % 2) + 1;
    
                switch (temp)
                {
                       case 1:
                            terrain[i][j] = 'G';
                            break;
                       case 2:
                            terrain[i][i] = 'W';
                            break;
                       default:
                            terrain[i][j] = 'A';
                            break;
                }
            }
        }
        
        for (int i = 0;i < 5; i++)
        {
            cout << "\n";
            for (int j = 0;j < 5; j++)
            {
                cout << terrain[i][j] << "\t";
            }
        }
    But the problem is a get some characters i want, plus i get some unexpected characters, i've played with the rand() function but i cant seem to figure out what im doing wrong, some help would be appreciated, thanks

  2. #2
    and the hat of wrongness Salem's Avatar
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    Surely you're not expecting any 'A's with that code?

    > terrain[i][i] = 'W';
    Oh, and check the subscripts here - seems a little lacking on the J front
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  3. #3
    Senior Member joshdick's Avatar
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    int temp = (rand() % 2) + 1;

    temp can only ever be 1 or 2, so I don't think you'll ever get any A's.

    Could you provide a sample output?

  4. #4
    Let's do some coding! Welshy's Avatar
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    ah a simple friggin typo! I only put the 'A' in there to see if it was the rand() causing my problems and generating numbers i didnt want, thanks for that

    new lesson learnt - proof-read code first :P

    **edit** i only wanted temp to be a 1 or 2

  5. #5
    Senior Member joshdick's Avatar
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    To prevent undefined behaviour from a typo, you could've intialised your variable.

  6. #6
    Let's do some coding! Welshy's Avatar
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    what do you mean? i initialised it in the loop

  7. #7
    Senior Member joshdick's Avatar
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    I mean initializing it with pre-determined values. For example, setting each char in the array equal to '_'. Then when you try filling the array with other values latter on, if you see any underscores in your output, it's likely that you haven't successfully written to those parts of the array.

  8. #8
    Let's do some coding! Welshy's Avatar
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    yeah that's what the 'A' was for, if i wasnt getting the values i wanted then it would print 'A', but i see what you mean, ill remember to try that one out

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