Added exponentialFunction for exponential calculations

src/main/c/main_taschenrechner.c

@@ -55,6 +55,13 @@ double logarithmBase2Function(double x) {
     // Logarithm with base 2
     return log2(x);
 }
+//..
+// Exponential function
+double exponentialFunction(double x) {
+    // Exponential function (e^x)
+    return exp(x);
+}
+
 
 // scientificmode
 int scientificMode(){

src/main/c/taschenrechner.h

@@ -24,6 +24,10 @@ double naturalLogarithmFunction(double x);
 
 double logarithmBase2Function(double x);
 
+//..
+// Exponential function
+double exponentialFunction(double x);
+
 int mode(int userChoice);
 
 int displayMenu();