diff --git a/matrix.c b/matrix.c
index 7ea5ead..045b601 100644
--- a/matrix.c
+++ b/matrix.c
@@ -73,25 +73,75 @@ Matrix createMatrix(size_t cols, size_t rows)
 
 void clearMatrix(Matrix *matrix)
 {
+    for (int i = 0; i < matrix->rows; i++) {
+        for (int j = 0; j < matrix->cols;j++) {
+            matrix->buffer[i-1 + matrix->rows*(j-1)] = UNDEFINED_MATRIX_VALUE;
+        }
+    }
+    free(matrix->buffer);
+    matrix->rows = 0;
+    matrix->cols = 0;
     
 }
 
 void setMatrixAt(MatrixType value, Matrix matrix, unsigned int rowIdx, unsigned int colIdx)
 {
-    
+    matrix.buffer[rowIdx-1 + matrix.rows*(colIdx-1)] = value;
 }
 
 MatrixType getMatrixAt(const Matrix matrix, unsigned int rowIdx, unsigned int colIdx)
 {
-    
+    MatrixType returnVal;
+    returnVal = matrix.buffer[rowIdx-1 + matrix.rows*(colIdx-1)];
+    return returnVal;
 }
 
 Matrix add(const Matrix matrix1, const Matrix matrix2)
 {
-    
+    //check if the matrices are able to be added (same size)
+    if (matrix1.cols == matrix2.cols && matrix1.rows == matrix2.rows){
+        //size of the matrices should be the same, if the addition is supposed to happen
+        Matrix outputMatrix = createMatrix(matrix1.rows, matrix1.cols);
+        for (int i = 0; i < matrix1.rows;i++) {
+            for (int j = 0; j < matrix1.cols; j++) {
+                // how this should work in normal Matrix version:
+                // outputmatrix.buffer[i][j] = matrix1.buffer[i][j] + matrix2.buffer[i][j];
+                outputMatrix.buffer[i + outputMatrix.rows* j] = matrix1.buffer[i + matrix1.rows* j] + matrix2.buffer[i + matrix2.rows * j];
+            }
+        }
+        return outputMatrix;
+    } else {
+        //the matrix could not be added, since the matrix sizes are not set correct.
+        Matrix m;
+        m.rows = 0; 
+        m.cols = 0;
+        m.buffer = NULL;
+        return m;
+    }
+
 }
 
 Matrix multiply(const Matrix matrix1, const Matrix matrix2)
 {
-    
+    //check, if the matrices can be multiplied
+    if (matrix1.rows == matrix2.cols) {
+        Matrix outputMatrix = createMatrix(matrix1.rows, matrix2.cols);
+        for(int i = 0; i < matrix1.rows; i++) {
+            for (int j = 0; j < matrix2.cols; j++) {
+                for (int k = 0; k < matrix2.rows; k++) {
+                    // how this should work in normal Matrix version:
+                    // outputMatrix.buffer[i][j] = matrix1.buffer[i][k] * matrix2.buffer[k][j];
+                    outputMatrix.buffer[i + outputMatrix.rows* j] = matrix1.buffer[i + matrix1.rows* k] * matrix2.buffer[k + matrix2.rows*j];
+                }
+            }
+        }
+        return outputMatrix;
+    } else {
+        //the matrix could not be added, since the matrix sizes are not set correct.
+        Matrix m;
+        m.rows = 0; 
+        m.cols = 0;
+        m.buffer = NULL;
+        return m;
+    }
 }
\ No newline at end of file
diff --git a/matrix.h b/matrix.h
index e89fdc7..8f05f79 100644
--- a/matrix.h
+++ b/matrix.h
@@ -7,8 +7,8 @@ typedef float MatrixType;
 // TODO Matrixtyp definieren
 
 typedef struct Matrix {
-    size_t rows;
-    size_t cols;
+    size_t rows; //X-Element
+    size_t cols; //Y-Element
     MatrixType *buffer;
 } Matrix;