3. (Program) Write a C++ program that accepts a string from the user and then replaces all occurrences of the letter e with the letter x. 4. (Useful utility) Modify the program written for Exercise 3 to search for the first occurrence of a user-entered sequence of characters, and then replace this sequence, when it's found in the string, with a second user-entered sequence. For example, if the entered string is Figure 4-4 illustrates the output of Program 4-2 and the user enters that 4- is to be replaced by 3-, the resulting string is Figure 3-4 illustrates the output of Program 4-2. (Only the first occurrence of the searched-for sequence has been changed.) 5. (Useful utility) Modify the program written for Exercise 4 to replace all occurrences of the designated sequence of characters with the new sequence of characters. For example, if the entered string is Figure 4-4 illustrates the output of Program 4-2 and the user enters that 4- is to be replaced by 3-, the resulting string is Figure 3-4 illustrates the output of Program 3-2.

(Electrical eng.) a. The voltage gain of an amplifier is given by this formula: voltagegain=[275 23 2 +0.5 f 2 ]n f is the frequency in Hz. n is the number of stages in the amplifier. Using this formula, write, compile, and run a C++ program to determine the value of the voltage gain for a four-stage amplifier operating at a frequency of 120 Hz. Your program should produce the following display: At a frequency of xxxxx hertz, the voltage gain is yyyyy Your program should replace xxxxx with the frequency and yyyyy with the voltage gain. b. Manually check the value your program produces. After verifying that your program is working correctly, modify it to determine the voltage gain of a 12-stage amplifier operating at a frequency of 9500 Hz.

(Numerical) Write a program that tests the effectiveness of the rand() library function. Start by initializing 10 counters to 0, and then generate a large number of pseudorandom integers between 0 and 9. Each time a 0 occurs, increment the variable you have designated as the zero counter; when a 1 occurs, increment the counter variable that’s keeping count of the 1s that occur; and so on. Finally, display the number of 0s, 1s, 2s, and so on that occurred and the percentage of the time they occurred.

Mark the following statements as true or false: a. To use a predefined function in a program, you need to know only the name of the function and how to use it. (1) b. A value-returning function returns only one value. (2, 3) c. Parameters allow you to use different values each time the function is called. (2, 7, 9) d. When a return statement executes in a user-defined function, the function immediately exits. (3, 4) e. A value-returning function returns only integer values. (4) f. A variable name cannot be passed to a value parameter. (3, 6) g. If a C++ function does not use parameters, parentheses around the empty parameter list are still required. (2, 3, 6) h. In C + + , the names of the corresponding formal and actual parameters must be the same. (3, 4, 6) i. A function that changes the value of a reference parameter also changes the value of the actual parameter. (7) j. Whenever the value of a reference parameter changes, the value of the actual parameter changes. (7) k. In C++, function definitions can be nested; that is, the definition of one function can be enclosed in the body of another function. (9) l. Using global variables in a program is a better programming style than using local variables, because extra variables can be avoided. (10) m. In a program, global constants are as dangerous as global variables. (10) n. The memory for a static variable remains allocated between function calls. (11)

(Biology) The number of bacteria, B, in a culture that’s subject to refrigeration can be approximated by this formula: B=300000e0.032t e is Euler’s number 2.71828 (rounded to five decimal places). t is the time in hours the culture has been refrigerated. Using this formula, write, compile, and run a C++ program that prompts the user for a value of time, calculates the number of bacteria in the culture, and displays the result. For testing purposes, check your program by using a test input of 10 hours. After verifying your program, use it to determine the number of bacteria in the culture after 12, 18, 24, 36, 48, and 72 hours.

(General math) a. The volume, V, of a cylinder is given by this formula: V=r2L r is the cylinder’s radius, and L is its length. Using this formula, write a C++ function named cylvol() that accepts a cylinder’s radius and length and returns its volume. b. Include the function written in Exercise 5a in a working program. Make sure your function is called from main() and returns a value to main() correctly. Have main() use a cout statement to display the returned value. Test the function by passing various data to it.