C ++布尔语句错误（我认为）

Question

这个程序应该要求一个整数，如果你想加或减，然后另一个整数，然后做数学，但它声明减法和加法作为错误输入，我认为我的布尔值有错误。任何帮助表示赞赏。

            /***********************************************************
        Program Name: Simple Math Calculator
        Program Author: Kyle NoCompile
        Date Created: 9/12/16
        Program Description:
            This program performs simple arithmetic calculations.
            The user enters numbers and the math operation to
            perform on those numbers. The program will then display
            the result of the operation.

        Modified Date:
        Modified Description:
        ***********************************************************/

        #include <iostream>
        using namespace std;

        // Function prototypes:
        void showWelcome();
        int getUserIntegerInput();
        char getMathChoice();
        int getInteger(bool);
        bool validateMathChoice(char choice);
        int doAddition(int int1, int int2);
        int doSubtraction(int int1, int int2);
        int doMath(int firstInt, int secondInt, char mathFunc);
        int showResult();


        // This is the main function (where the program begins)
        int main()
        {
            // Variables to hold local data
            int firstNum;
            int secondNum;
            int mathChoice;
            int result;

            // Call the showWelcome() function
            void showWelcome();

            // Call the getInteger() function (for the first integer)
            // and store the result in the "firstNum" variable
            firstNum = getInteger(true);


            // Call the getMathChoice() function and store result in "mathChoice" variable
            mathChoice = getMathChoice();

            // Call validateMathChoice() function, passing it the user's math choice
            // and using the return value to decide what to do next
            if (validateMathChoice() = true)
            {
                // Call the getInteger() function (for the second and subsequent integers)
                // and store the result in the "secondNum" variable
                secondNum = getInteger(false);

                // Call the doMath() function and pass it all of the user input
                // and store the return value in the "result" variable.
                int result = doMath(firstNum,secondNum,mathChoice);

                // Call the showResult() function to show the result
                int showResult(int result);
            }
            else
            {
                // If the user chose an invalid math function...
                cout<<"Not a valid math choice"<<endl;
            }

            return 0;
        }


        // This function shows a nice welcome message
        void showWelcome()
        {
            cout<<"******************************************"<<endl;
            cout<<"Welcome to the simple calculator program!"<<endl;
            cout<<"This program will do simple addition and"<<endl;
            cout<<"subtraction. Math is fun, so enjoy!"<<endl;
            cout<<"******************************************"<<endl;
        }

        // This function gets integer input from the user
        int getUserIntegerInput()
        {
            int input;
            cin>>input;
            return input;
        }

        // This function asks the user for a math function
        // and returns the user's input
        char getMathChoice()
        {
            char choice;
            cout<<endl<<"Please select a math function to perform (\"+\" = Addition, \"-\" = Subtraction): ";
            cin>>choice;
            return choice;
        }

        // this function asks the user for either the first integer
        // or the second and returns the user's input
        int getInteger(bool firstNum)
        {
            cout<<endl<<"Please enter the ";

            // if the "firstNumber" variable is true, then this
            // is the first number being collected
            if (firstNum)
            {
                cout<<"first ";
            }
            // Otherwise, it's the second number being collected
            else
            {
                cout<<"second ";
            }

            cout<<"integer: ";

            // Call the getUserIntegerInput() function and return the return value from it
            return getUserIntegerInput();
        }



        // This function validates the user's match function choice
        // by returning a true for valid, and a false for invalid
        bool validateMathChoice(char choice)
        {
            if (choice == '+' || choice == '-')
            {
                return true;
            }
            else
            {
                return false;
            }
        }

        // This function adds two integers
        int doAddition(int firstInt,int secondInt)
        {
            return firstInt + secondInt;
        };

        // This function subtracts the second integer
        // parameter from the first integer parameter
        int doSubtraction(int firstInt, int secondInt)
        {
            return firstInt - secondInt;
        };


        // This function determines the result of the math
        // operation requested by the user
        int doMath(int firstInt, int secondInt, char mathFunc)
        {
            // Initialize result to zero (0)
            int result = 0;

            // If the math function is a "+", then call the
            // doAddition() function and store the return
            // value in the "result" variable
            if (mathFunc = '+')
            {
                result = doAddition(firstInt, secondInt);
                return result;
            }
            // If the math function is a "-", then call the
            // doSubtraction() function and store the return
            // value in the "result" variable
            else (mathFunc = '-');
            {
                result = doSubtraction(firstInt, secondInt);
                return result;
            }

            return result;
        }

        // This function displays the result of a math operation
        int showResult(int result)
        {
            cout<<endl<<"The result is "<<result<<endl;
        }