Write C++ programs using a single main function. Hint:for each problem write a test function for it then call thesetest functions in the main function. Section 2.3 12. Write a C++ function: int rectArea (int len, int wid) that returns the area of a rectangle with length len and width wid. Test it inside the main program that inputs the length and width of a rectangle and outputs its area. Output the value in the main program, not in the function. 13. Write a C++ function void rect (int& ar, int& per, int len, int wid) that computes the area ar and perimeter per of a rectangle with length len and width wid. Test it inside the main program that inputs the length and width of a rectangle and outputs its area and perimeter. Output the value in the main program, not in the procedure. Section 2.4 14. Write a C++ recursive function int fib(int n) that returns the value of the n’th Fibonacci number. Do not use a loop. Test it in the main program, not in the function. The Fibonacci sequence is 0 1 1 2 3 5 8 13 21... Each Fibonacci nu ber the sum of the preceding Fibonacci nur //Lab1.cpp // add statement to include iostream // add statement to use namespace std // declare all functions except main function here int rectArea (int len, int wid); void testExercise12(); void rect (int & ar, int& per, int len, int wid); void testExercise13(); Int main() { cout << "Lab1: your real names" << endl; cout << "Test exercise 12: " << endl; test Exercise12(); return 0; } #Implement all functions you have declared here. Section 2.3 12. Write a CH function int rectArea (int len, int wid) that returns the area of a rectangle with length len and width wid. Test it with a main program that inputs the length and width of a rectangle and outputs its area. Output the value in the main program, not in the function, Sample Input 6 10 Sample Output The area of a 6 by 10 rectangle is 60. 13. Write a CH function void rect (int& ar, int& per, int len, int wid) that computes the area ar and perimeter per of a rectangle with length len and width wid. Test it with a main program that inputs the length and width of a rectangle and outputs its area and perimeter. Output the value in the main program, not in the procedure. Sample Input 6 10 Sample Output Length: 6 Width: 10 Area: 60 Perimeter: 32 Section 2.4 14. Write a CH program that asks the user to input a small integer. Then use a recursive function that returns the value of that Fibonacci number as defined in Exercise 5. Do not use a loop. Output the value in the main program not in the function, Sample Input/Output Which Fibonacct number? 8 The number is 21