added if clause to check for fittig matrix dimensions

matrix.c

@@ -38,5 +38,24 @@ Matrix add(const Matrix matrix1, const Matrix matrix2)
 
 Matrix multiply(const Matrix matrix1, const Matrix matrix2)
 {
+    if (matrix1.rows == matrix2.cols) {
+        Matrix result;
+	    result.rows = matrix1.rows;
+        result.cols = matrix2.cols;
 
+        result.buffer = malloc(result.rows * result.cols * sizeof(MatrixType));
+
+        for(int i = 0; i < rows; i++) {
+            for(int j = 0; j < cols; j++) {
+                MatrixType value = 0;
+                for(int k = 0; k < matrix1.cols; k++) {
+                    value += matrix1[i][k] * matrix2[k][j];
+                }
+                result.buffer[i][i] = value;
+            }
+        }
+        return result;
+    }
+    printf("Die angegebenen Matrizen haben keine passenden Dimensionen für die Multiplikation");
+    return NULL;
 }