Attempting to create a rudimentary calculator with C++; Getting a high amount of compilation errors

Question

I am incredibly new to programming and this is my first attempting at doing anything. I believe I had declared everything properly as well as the if statements, however I get multiple compilation errors that do not make any sense, as I cannot parse what they are trying to say is wrong with the code. I am incredibly confused and I want to learn what I am doing wrong.

Here is a list:

1. main.cpp: In function ‘int main()’:
main.cpp:28:19: error: expected primary-expression before ‘answer’
     cin >> string answer;
                   ^
2. main.cpp:30:19: error: ‘add’ was not declared in this scope
     if (answer == add)
                   ^
3. main.cpp:31:13: error: redeclaration of ‘int add’
     int add(answer1,answer2);
             ^
4. main.cpp:30:19: note: ‘add’ previously declared here
     if (answer == add)
                   ^
5. main.cpp:31:13: error: ‘answer1’ was not declared in this scope
     int add(answer1,answer2);
             ^
6. main.cpp:31:21: error: ‘answer2’ was not declared in this scope
     int add(answer1,answer2);
                     ^
7. main.cpp:31:28: error: expression list treated as compound expression in initializer [-fpermissive]
     int add(answer1,answer2);
                            ^
8. main.cpp:33:5: error: ‘else’ without a previous ‘if’
     else if (answer == subtract)
     ^
9. main.cpp:33:24: error: ‘subtract’ was not declared in this scope
     else if (answer == subtract)
                        ^
10. main.cpp:34:18: error: redeclaration of ‘int subtract’
     int subtract(answer1,answer2);
                  ^
11. main.cpp:33:24: note: ‘subtract’ previously declared here
     else if (answer == subtract)
                        ^
12. main.cpp:34:18: error: ‘answer1’ was not declared in this scope
     int subtract(answer1,answer2);
                  ^
13. main.cpp:34:26: error: ‘answer2’ was not declared in this scope
     int subtract(answer1,answer2);
                          ^
14. main.cpp:34:33: error: expression list treated as compound expression in initializer [-fpermissive]
     int subtract(answer1,answer2);
                                 ^
15. main.cpp:36:5: error: ‘else’ without a previous ‘if’
     else if (answer == multiply)
     ^
16. main.cpp:36:24: error: ‘multiply’ was not declared in this scope
     else if (answer == multiply)
                        ^
17. main.cpp:37:18: error: redeclaration of ‘int multiply’
     int multiply(answer1,answer2);
                  ^
18. main.cpp:36:24: note: ‘multiply’ previously declared here
     else if (answer == multiply)
                        ^
19. main.cpp:37:18: error: ‘answer1’ was not declared in this scope
     int multiply(answer1,answer2);
                  ^
20. main.cpp:37:26: error: ‘answer2’ was not declared in this scope
     int multiply(answer1,answer2);
                          ^
21. main.cpp:37:33: error: expression list treated as compound expression in initializer [-fpermissive]
     int multiply(answer1,answer2);
                                 ^
22. main.cpp:39:5: error: ‘else’ without a previous ‘if’
     else if (answer == divide)
     ^
23. main.cpp:39:24: error: ‘divide’ was not declared in this scope
     else if (answer == divide)
                        ^
24. main.cpp:40:16: error: redeclaration of ‘int divide’
     int divide(answer1,answer2);
                ^
25. main.cpp:39:24: note: ‘divide’ previously declared here
     else if (answer == divide)
                        ^
26. main.cpp:40:16: error: ‘answer1’ was not declared in this scope
     int divide(answer1,answer2);
                ^
27. main.cpp:40:24: error: ‘answer2’ was not declared in this scope
     int divide(answer1,answer2);
                        ^
28. main.cpp:40:31: error: expression list treated as compound expression in initializer [-fpermissive]
     int divide(answer1,answer2);
                               ^
29. main.cpp:42:5: error: ‘else’ without a previous ‘if’
     else if
     ^
30. main.cpp:43:5: error: expected ‘(’ before ‘cout’
     cout << "Invalid Option!";
     ^
31. main.cpp: At global scope:

32. main.cpp:50:14: error: ‘a’ was not declared in this scope
 int subtract(a,b);
              ^
33. main.cpp:50:16: error: ‘b’ was not declared in this scope
 int subtract(a,b);
                ^
34. main.cpp:50:17: error: expression list treated as compound expression in initializer [-fpermissive]
 int subtract(a,b);
                 ^
35. main.cpp:51:1: error: expected unqualified-id before ‘{’ token
 {
 ^
36. main.cpp:56:14: error: ‘a’ was not declared in this scope
 int multiply(a,b);
              ^
37. main.cpp:56:16: error: ‘b’ was not declared in this scope
 int multiply(a,b);
                ^
38. main.cpp:56:17: error: expression list treated as compound expression in initializer [-fpermissive]
 int multiply(a,b);
                 ^
39. main.cpp:57:1: error: expected unqualified-id before ‘{’ token
 {
 ^
40. main.cpp:62:9: error: ‘a’ was not declared in this scope
 int add(a,b);
         ^
41. main.cpp:62:11: error: ‘b’ was not declared in this scope
 int add(a,b);
           ^
42. main.cpp:62:12: error: expression list treated as compound expression in initializer [-fpermissive]
 int add(a,b);
            ^
43. main.cpp:63:1: error: expected unqualified-id before ‘{’ token
 {
 ^
44. main.cpp:68:12: error: ‘a’ was not declared in this scope
 int divide(a,b);
            ^
45. main.cpp:68:14: error: ‘b’ was not declared in this scope
 int divide(a,b);
              ^
46. main.cpp:68:15: error: expression list treated as compound expression in initializer [-fpermissive]
 int divide(a,b);
               ^
47. main.cpp:69:1: error: expected unqualified-id before ‘{’ token
 {
 ^

Here is the code:

#include <iostream>
using namespace std;

int main()
{

int number1;
int number2;
string answer;
int result;
int a;
int b;


cout << "Enter first number" << endl;
cin >> number1;
cout << "Enter second number" << endl;
cin >> number2;
cout << "What would you like to do?" << endl << "Options: Add, substract, 
multiply, divide" << endl;
cin >> string answer;

if (answer == add)
int add(answer1,answer2);
 cout << result;
else if (answer == subtract)
int subtract(answer1,answer2);
 cout << result;
else if (answer == multiply)
int multiply(answer1,answer2);
 cout << result;
else if (answer == divide)
int divide(answer1,answer2);
cout << result;
else if
cout << "Invalid Option!";
return 0;

}



int subtract(a,b);
{
 result = a-b;
 return result;   
}

int multiply(a,b);
{
    cout << a*b;
}

int add(a,b);
{
cout << a+b;
}

int divide(a,b);
{
    cout << a/b;
 }

Answer 1

Don't give up! Try starting from the beginning. Move slowly.

#include <iostream>
#include <string>

/*
This is regarded as bad practice...
From Python's `import this`:
   Namespaces are one honking great idea -- let's do more of those!
*/
using namespace std;

// Define your function
int add(int a, int b);

int main()
{

    int number1, number2, result;
    string answer;

    cout << "Enter first number" << endl;
    cin >> number1;
    cout << "Enter second number" << endl;
    cin >> number2;
    cout << "What would you like to do?" << endl << "Options: Add, substract, multiply, divide" << endl;
    cin >> answer;

    cout << "You chose: " << answer << endl;

    // Can this handle lowercase "add"? If not, how do you fix it?
    if (answer == "Add") {
        result = add(number1,number2);
        cout << number1 << " + " << number2 << " = " << result << endl;
    }
    // What about divide, multiply, etc.?
    // That's an exercise left to the reader ;)

}

int add(int a, int b) {
    return a + b;
}

This produces:

Enter first number
12

Enter second number
12

What would you like to do?
Options: Add, substract, multiply, divide
Add

You chose: Add
12 + 12 = 24

Answer 2

Instead of cin >> string answer; use cin >> answer;. You've a;ready got answer declared, so declaring it here is not necessary (and actually not legal). Other than that your add, subtract, multiply and divide functions are declared too soon. Add declarations or move those function definitions before main. You've got extra ; signs after between function declaration and it's body and you're missing types of functions arguments

int subtract(a,b); // delete ; here and add int (or better float) before a and b
{
 result = a-b; // you need to declare result, add type before this line (int or float, float would be better
 return result;   
}

Also number1 and number2 should be at least floats (or doubles), otherwise you're gonna have a bad time with division operations.

Hit me up if you've got more questions about it.

Answer 3

cin >> string answer; doesn't make sense. string answer is not an expression, so you can't use it as the right-hand operand of the >> operator.

You probably meant cin >> answer; because string answer; was already declared earlier in the function.

Also, you're missing #include <string>.

(This answer only covers the first error. I usually only look at the first error message, fix the code, then compile again. In your case there seems to be a lot more wrong with the code. Sorry.)