diff --git a/matrix.c b/matrix.c
index 8da5a94..55d3dd5 100644
--- a/matrix.c
+++ b/matrix.c
@@ -40,20 +40,74 @@ void clearMatrix(Matrix *matrix)
 
 void setMatrixAt(MatrixType value, Matrix matrix, unsigned int rowIdx, unsigned int colIdx)
 {
-    
+    if (rowIdx >= matrix.rows || colIdx >= matrix.cols) {
+        fprintf(stderr, "Error: setMatrixAt index out of bounds.\n");
+        return;
+    }
+
+    matrix.buffer[rowIdx * matrix.cols + colIdx] = value;
 }
 
 MatrixType getMatrixAt(const Matrix matrix, unsigned int rowIdx, unsigned int colIdx)
 {
-    
+    if (rowIdx >= matrix.rows || colIdx >= matrix.cols) {
+        fprintf(stderr, "Error: getMatrixAt index out of bounds.\n");
+        return UNDEFINED_MATRIX_VALUE;
+    }
+
+    return matrix.buffer[rowIdx * matrix.cols + colIdx];
 }
 
 Matrix add(const Matrix matrix1, const Matrix matrix2)
 {
-    
+    if (matrix1.rows != matrix2.rows || matrix1.cols != matrix2.cols) {
+        fprintf(stderr, "Error: Matrix dimensions do not match for addition.\n");
+        Matrix empty = {0, 0, NULL};
+        return empty;
+    }
+
+    Matrix result = createMatrix(matrix1.rows, matrix1.cols);
+    if (result.buffer == NULL) {
+        return result;
+    }
+
+    for (unsigned int i = 0; i < matrix1.rows; i++) {
+        for (unsigned int j = 0; j < matrix1.cols; j++) {
+            setMatrixAt(
+                getMatrixAt(matrix1, i, j) + getMatrixAt(matrix2, i, j),
+                result,
+                i, j
+            );
+        }
+    }
+
+    return result;
 }
 
 Matrix multiply(const Matrix matrix1, const Matrix matrix2)
 {
-    
+  if (matrix1.cols != matrix2.rows) {
+        fprintf(stderr, "Error: Invalid matrix dimensions for multiplication.\n");
+        Matrix empty = {0, 0, NULL};
+        return empty;
+    }
+
+    Matrix result = createMatrix(matrix1.rows, matrix2.cols);
+    if (result.buffer == NULL) {
+        return result;
+    }
+
+    for (unsigned int i = 0; i < matrix1.rows; i++) {
+        for (unsigned int j = 0; j < matrix2.cols; j++) {
+            MatrixType sum = 0.0f;
+
+            for (unsigned int k = 0; k < matrix1.cols; k++) {
+                sum += getMatrixAt(matrix1, i, k) * getMatrixAt(matrix2, k, j);
+            }
+
+            setMatrixAt(sum, result, i, j);
+        }
+    }
+
+    return result;
 }
\ No newline at end of file
diff --git a/neuralNetwork.c b/neuralNetwork.c
index bd8f164..1e9dce8 100644
--- a/neuralNetwork.c
+++ b/neuralNetwork.c
@@ -170,7 +170,7 @@ NeuralNetwork loadModel(const char *path)
 
 static Matrix imageBatchToMatrixOfImageVectors(const GrayScaleImage images[], unsigned int count)
 {
-    Matrix matrix = {NULL, 0, 0};
+    Matrix matrix = {NULL, 0, 0}; //hier evtl Null auf int casten?
 
     if(count > 0 && images != NULL)
     {