diff --git a/src/main/c/main_taschenrechner.c b/src/main/c/main_taschenrechner.c
index 79ece02..f1fccac 100644
--- a/src/main/c/main_taschenrechner.c
+++ b/src/main/c/main_taschenrechner.c
@@ -1,12 +1,229 @@
 #include <stdio.h>
-// #include <string.h>
+#include <string.h>
 #include <stdlib.h>
+#include <math.h>
 
 #include "taschenrechner.h"
 
 
-int add(int a, int b) {
+doulbe add(doulbe a, doulbe b) {
+    return a + b;
+}
+
+doulbe minus (doulbe a, doulbe b){
+    return a - b;
+}
+
+doulbe multiply(doulbe a, doulbe b) {
+    return a * b;
+}
+
+doulbe divide(doulbe a, doulbe b) {
+    if (b == 0) {
+        return 0;
+    }
+    return a / b;
+}
+
+// Square root function
+double squareRootFunction(double x) {
+    // Using the sqrt function from math.h
+    return sqrt(x);
+}
+
+//..
+// Trigonometric functions
+double sineFunction(double angle) {
+    // Convert degrees to radians for trigonometric functions
+    return sin(angle * M_PI / 180.0);
+}
+
+
+double cosineFunction(double angle) {
+    // Convert degrees to radians for trigonometric functions
+    return cos(angle * M_PI / 180.0);
+}
+
+double tangentFunction(double angle) {
+    // Convert degrees to radians for trigonometric functions
+    return tan(angle * M_PI / 180.0);
+}
+
+//..
+// Logarithmic functions
+double logarithmFunction(double x) {
+    // Logarithm with base 10
+    return log10(x);
+}
+
+double naturalLogarithmFunction(double x) {
+    // Natural logarithm (ln)
+    return log(x);
+}
+
+double logarithmBase2Function(double x) {
+    // Logarithm with base 2
+    return log2(x);
+}
+//..
+// Exponential function
+double exponentialFunction(double x) {
+    // Exponential function (e^x)
+    return exp(x);
+}
+
+// ..
+// Bitwise AND function
+int bitwiseAND(int num1, int num2) {
+    return num1 & num2;
+}
+
+// Bitwise OR function
+int bitwiseOR(int num1, int num2) {
+    return num1 | num2;
+}
+
+// Bitwise XOR function
+int bitwiseXOR(int num1, int num2) {
+    return num1 ^ num2;
+}
+
+//..
+
+// scientificmode
+int scientificMode(){
+
+    double num, result;
+
+    int choice;
+
+    printf("Enter a number: ");
+
+    scanf("%lf", &num); // scan the number from user
     
-    return a+b;
+    printf("Scientific mode Options:\n");
+    printf("1: Square root:\n");
+    printf("2: Exponential:\n");
+    printf("2: Logarithm:\n");
+    printf("4: Trigonomertic");
+    scanf("%d", &choice); // user choice
+
+    switch(choice) {
+
+        case 1: // Square root
+        break;
+
+        case 2: // Exponential
+        break;
+
+        case 3: // Logarithm
+        break;
+
+        case 4: // Trigonomertic 
+        break;
     
+        default: printf("Invalid choice. Please try again.\n");
+
+    }
+
+    return result;
+}
+
+// graphMode
+void graphMode() {
+    double x, y;
+
+    printf("Enter the range for x (start end step): ");
+    double x_start, x_end, x_step;
+    scanf("%lf %lf %lf", &x_start, &x_end, &x_step);
+
+    printf("\nGraph for the function y = sin(x):\n");
+
+    printf(" x\t| y\n");
+    printf("--------------\n");
+
+    for (x = x_start; x <= x_end; x += x_step) {
+        y = sin(x);
+        printf("%.2lf\t| %.2lf\n", x, y);
+    }
+}
+
+// Programming mode
+
+void programmingMode() {
+
+    int num1, num2, result;
+    char operator;
+
+    printf("Enter first integer: ");
+    scanf("%d", &num1);
+
+    printf("Enter operator (+, -, *, /): ");
+    scanf(" %c", &operator);
+
+    printf("Enter second integer: ");
+    scanf("%d", &num2);
+
+}
+
+// Unit converter mode
+
+void unitConverterMode() {
+    int choice;
+    double value, result;
+
+    printf("Unit Converter Mode:\n");
+    printf("1. Meter to Kilometer\n");
+    printf("2. Kilogram to Gram\n");
+    printf("3. Celsius to Fahrenheit\n");
+    printf("Enter your choice: ");
+    scanf("%d", &choice);
+
+    printf("Enter the value to convert: ");
+    scanf("%lf", &value);
+
 }
+
+// change mode
+int mode(int userChoice){
+
+    switch(userChoice) {
+
+        case 1:return 1; // Basic mode
+        break;
+
+        case 2:return 2; // Scientific mode (Trigonomertic functions, Logarithm and exponential functions.)
+        break;
+
+        case 3:return 3; // Graph mode (Draw and visualize functions.)
+        break;
+
+        case 4:return 4; // Programming mode (Binary , octal and hexadecimal )
+        break;
+
+        case 5:return 5; // Unit converter mode (length, weight volume etc.)
+        break;
+
+        case 0: return 0; // printf("Exiting the calculator.\n");
+        break;
+        
+        default: return -1; // printf("Invalid choice. Please try again.\n");
+
+    }
+
+}
+
+
+// display the mode options:
+int displayMenu(){
+
+    printf("\nCalculator Modes: \n");
+    printf("\n1: Basic Mode\n");
+    printf("\n2: Scientific Mode (Trigonomertic functions, Logarithm and exponential functions.)\n");
+    printf("\n3: Graph Mode (Draw and visualize functions.)\n");
+    printf("\n4: Programming Mode (Binary , octal and hexadecimal )\n");
+    printf("\n5: Unit converter Mode (length, weight volume etc.)\n");
+    printf("\n0: Exit calculator\n");
+
+    return 1; // return 1 to check if the function works 
+}
\ No newline at end of file
diff --git a/src/main/c/taschenrechner.h b/src/main/c/taschenrechner.h
index 1261fd7..7b548f9 100644
--- a/src/main/c/taschenrechner.h
+++ b/src/main/c/taschenrechner.h
@@ -1,6 +1,49 @@
 #ifndef TASCHENRECHNER_H
 #define TASCHENRECHNER_H
 
-int add(int a, int b);
+doulbe add(doulbe a, doulbe b);
+
+doulbe minus(doulbe a, doulbe b);
+
+doulbe multiply(doulbe a, doulbe b);
+
+doulbe divide(doulbe a, doulbe b);
+
+// Square root function
+double squareRootFunction(double x);
+
+//..
+// Trigonometric functions
+double sineFunction(double angle);
+
+double cosineFunction(double angle);
+
+double tangentFunction(double angle);
+
+//..
+// Logarithmic functions
+double logarithmFunction(double x);
+
+double naturalLogarithmFunction(double x);
+
+double logarithmBase2Function(double x);
+
+//..
+// Exponential function
+double exponentialFunction(double x);
+
+// ..
+// Bitwise AND function
+int bitwiseAND(int num1, int num2);
+
+// Bitwise OR function
+int bitwiseOR(int num1, int num2);
+
+// Bitwise XOR function
+int bitwiseXOR(int num1, int num2);
+
+int mode(int userChoice);
+
+int displayMenu();
 
 #endif // TASCHENRECHNER_H