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POWhy did I need to use this statement twice - Matrix Multiplication
 

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  1. POWhy did I need to use this statement twice - Matrix Multiplication
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    <p>I was developing a program to find matrix multiplication.</p> <pre><code>#include &lt;iostream&gt; using namespace std; int main() { int a=0,b=0,c=0,d=0,e=0; cout&lt;&lt;"Enter the order of the first matrix A \n\nNumber of Rows : "; cin&gt;&gt;a; cout&lt;&lt;"\nNumber of Columns : "; cin&gt;&gt;b; cout&lt;&lt;endl; int matrixA[a][b]; cout&lt;&lt;"Enter the matrix Elements "&lt;&lt;endl; for(int m=0; m&lt;a; m++) { for(int n=0; n&lt;b; n++) { cout&lt;&lt;"A ("&lt;&lt; m+1 &lt;&lt;" , "&lt;&lt;n+1&lt;&lt;" ) ="; cin&gt;&gt;matrixA[m][n]; //cout&lt;&lt;","; } cout&lt;&lt;endl; } ////////////////////////// Startup cout&lt;&lt;"Enter the order of the Second matrix A \n\nNumber of Rows : "&lt;&lt;b; c=b; cout&lt;&lt;"\nNumber of Columns : "; cin&gt;&gt;d; cout&lt;&lt;endl; int matrixB[c][d]; cout&lt;&lt;"Enter the matrix Elements "&lt;&lt;endl; for(int p=0; p&lt;c; p++) { for(int q=0; q&lt;d; q++) { cout&lt;&lt;"B ("&lt;&lt; p+1 &lt;&lt;" , "&lt;&lt;q+1&lt;&lt;" ) ="; cin&gt;&gt;matrixB[p][q]; //cout&lt;&lt;","; } cout&lt;&lt;endl; } ///////////// initialisting matrixAns int matrixAns[a][d]; for(int p=0; p&lt;a; p++) { for(int q=0; q&lt;d; q++) { matrixAns[p][q]=0; } } //////////////////// finding ans for(int r=0; r&lt;a; r++) { for(int s=0; s&lt;d; s++) { for(int t=0; t&lt;b; t++) { e = matrixA[r][t]*matrixB[t][s]; } matrixAns[r][s] = e+matrixAns[r][s]; matrixAns[r][s] = e+matrixAns[r][s]; //dont know why i have to add this same code again } } ////////////////////// Ans Printing cout&lt;&lt;"\nMatrix Multiplication Answer \n"&lt;&lt;endl; for(int h=0; h&lt;a; h++) { for(int i=0; i&lt;d; i++) { cout&lt;&lt;" "&lt;&lt;matrixAns[h][i]&lt;&lt;" "; } cout&lt;&lt;endl; } } </code></pre> <p>And one important thing: this is not my homework or assignment!</p> <p>The method that I have used works perfectly but it does not give me the right answer until I use this statement twice. (I got this by a trial and error method).</p> <pre><code>matrixAns[r][s] = e+matrixAns[r][s]; </code></pre> <p>I have also initailised the <code>matrixAns</code> by using a loop (and had set it to 0).</p> <p>I am new to C++ and want to know what was the error that I got and how the use of the two statements gives me correct answer. </p> <p>Is there any way to get rid of one of the statements without destroying the app?</p>
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    1. USArjun SK
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      1. POWhy did I need to use this statement twice - Matrix Multiplication
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    1. COIf you write it twice, it is equivalent to `matrixAns[r][s] = 2*e+matrixAns[r][s]`. is this want you want?
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    2. COI want to know how you got C++ to make arrays of non-constant values.
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    3. COThis is more flexible as it can find the multiple of any matrix that satisfies the basic condition!
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      1. POWhy did I need to use this statement twice - Matrix Multiplication
      1. USArjun SK
 

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