diff --git a/Startcode/matrix.c b/Startcode/matrix.c
index b238b81..07a2309 100644
--- a/Startcode/matrix.c
+++ b/Startcode/matrix.c
@@ -20,9 +20,9 @@ Matrix createMatrix(unsigned int rows, unsigned int cols)
 
 void clearMatrix(Matrix *matrix)
 {
-    for (int i = 0; i < matrix->rows; i++)
+    for (unsigned int i = 0; i < matrix->rows; i++)
     {
-        for (int j = 0; j < matrix->cols; j++)
+        for (unsigned int j = 0; j < matrix->cols; j++)
         {
             setMatrixElement(matrix, i, j, UNDEFINED_MATRIX_VALUE);
         }
@@ -43,11 +43,18 @@ Matrix add(const Matrix matrix1, const Matrix matrix2)
 {
     if (matrix1.rows != matrix2.rows || matrix1.cols != matrix2.cols)
     {
-        return matrix1;
+        fprintf(stderr, "Fehler: Dimensionen stimmen nicht überein (%ux%u und %ux%u)\n",
+                matrix1->rows, matrix1->cols, matrix2->rows, matrix2->cols);
+        return (Matrix){ .rows = 0, .cols = 0, .storage = NULL };
     }
 
     Matrix result = createMatrix(matrix1.rows, matrix1.cols);
 
+    // check, ob genügend Speicher vorhanden
+    if (result.storage == NULL) {
+        return (Matrix){ .rows = 0, .cols = 0, .storage = NULL };
+    }
+
     for (unsigned int i = 0; i < matrix1.rows; i++)
     {
         for (unsigned int j = 0; j < matrix1.cols; j++)
@@ -62,5 +69,36 @@ Matrix add(const Matrix matrix1, const Matrix matrix2)
 
 Matrix multiply(const Matrix matrix1, const Matrix matrix2)
 {
-    
+    if (matrix1.cols != matrix2.rows)
+    {
+        fprintf(stderr, "Fehler: Spalten von Matrix 1 (%u) entsprechen nicht Zeilen von Matrix 2 (%u)\n",
+                matrix1.cols, matrix2.rows);
+        return (Matrix){ .rows = 0, .cols = 0, .storage = NULL };
+    }
+
+    Matrix result = createMatrix(matrix1.rows, matrix2.cols);
+
+    // check, ob genügend Speicher vorhanden
+    if (result.storage == NULL) {
+        return (Matrix){ .rows = 0, .cols = 0, .storage = NULL };
+    }
+
+    for (unsigned int i = 0; i < matrix1.rows; i++)
+    {
+        for (unsigned int j = 0; j < matrix2.cols; j++)
+        {
+            MatrixType sum = 0;
+
+            for (unsigned int k = 0; k < matrix1.cols; k++)
+            {
+                MatrixType val1 = matrix1.storage[i * matrix1.cols + k];
+                MatrixType val2 = matrix2.storage[k * matrix2.cols + j];
+                sum += val1 * val2;
+            }
+
+            result.storage[i * result.cols + j] = sum;
+        }
+    }
+
+    return result;
 }
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