Programming output incorrect

[XxLooneyTunes]

Hi, so I'm writing this code for my c++ course that acts as a mini calculator by using <fstream> to refer to a txt file given to us with seven rows of two integers and a mathematical operator. We're told what to output for each operator. This is my code:

#include <iostream>
#include <fstream>
using namespace std;
int main(int argc, const char * argv[]) {

int first, second, i;
char mathOper;
ifstream calc;


calc.open ("calc.txt");



for(i=0;i<7;i++){

calc>>first>>second>>mathOper;

if(mathOper=='*')
cout<<first<<" * "<<second<<" = "<<first*second<<endl;
else if(mathOper=='/' && second=='0')
cout<<first<<" / "<<second<<" = infinity as denominator is zero <<endl;
else if(mathOper=='/')
cout<<first<<" / "<<second<<" = "<<first<<" % "<<second<<" = "<<first%second<<endl;
else if(mathOper=='+')
cout<<first<<" + "<<second<<" = "<<first+second<<endl;
else if(mathOper=='-')
cout<<first<<" - "<<second<<" = "<<first-second<<endl;
else
cout<<first<<" "<<mathOper<<" "<<second<<" = .....Invalid mathematical operator."<<endl;

}

calc.close();


return 0;
}

For some reason the output is always "0 0 = ...Invalid mathematical operator." even though the numbers in the calc.txt are not zero's, and its not showing the mathematical operator. I have the calc.txt in the same folder as the xcode file. Help please?

[Thomas1965]

Your program seems to work. Only problem is that it performs a modulo op when it should perform a division on lines

else if(mathOper=='/')
cout<<first<<" / "<<second<<" = "<<first<<" % "<<second<<" = "<<first%second<<endl;

Maybe you have a problem with your input file. The one I used was
1 2 +
2 3 -
3 4 /
5 5 *
1 1 +
2 2 +
1 3 /

OUTPUT

1 + 2 = 3
2 - 3 = -1
3 / 4 = 3 % 4 = 3
5 * 5 = 25
1 + 1 = 2
2 + 2 = 4
1 / 3 = 1 % 3 = 1

[XxLooneyTunes]

Turns out it was a mac problem and the input file was not being read. I've fixed it and it runs but I've encountered another problem. This is the file that is being read:

10 3 *
10 3 /
10 3 %
10 3 +
10 0 /
10 3 -
10 5 !
10 10 *

The program runs fine until it reaches the 5th line with zero as the denominator and I get the error message "Thread 1: EXC_ARITHMETIC(code = EXC_1386_DIV, subcode = (0x0)", and the code stops working. I think it's having a problem with the math because its not going to my

else if(mathOper=='/' && second=='0')
cout<<first<<" / "<<second<<" = infinity as denominator is zero <<endl; 

but rather is going to the line

else if(mathOper=='/')
cout<<first<<" / "<<second<<" = "<<first<<" % "<<second<<" = "<<first%second<<endl;

OUTPUT

10 * 3 = 30
10 / 3 = 10 % 3 = 1
10 % 3 = .....Invalid mathematical operator.
10 + 3 = 13
(lldb) 

Also to answer your question about the modulus operator being used instead of division, thats actually just what we were instructed to do so thats fine x)

Can anyone help?

[Thomas1965]

else if(mathOper=='/' && second=='0') should be else if(mathOper=='/' && second== 0)

[48T7M4Gy]

#include <iostream>
#include <fstream>


int main() {
    
    int first, second;
    char mathOper;
    
    std::ifstream calc;
    calc.open ("calc.txt");
    while( calc >> first >> second >> mathOper)
    {
        if(mathOper=='*')
            std::cout << first << " * " << second << " = " << first*second << std::endl;
        
        else if(mathOper=='/' && second == 0) // <-- ***
            std::cout << first << " / " <<second<< " = infinity as denominator is zero" << std::endl;
        
        else if(mathOper=='/' && second != 0) // <-- ***
            std::cout<<first<<" / "<<second<<" = "<<first<<" % "<<second<<" = "<<first%second<<std::endl;
        
        else if(mathOper=='+')
            std::cout<<first<<" + "<<second<<" = "<<first+second<<std::endl;
        
        else if(mathOper=='-')
            std::cout<<first<<" - "<<second<<" = "<<first-second<<std::endl;
        
        else
            std::cout << first << " " << mathOper << " " << second << " = .....Invalid mathematical operator." <<std::endl;
        
    }
    
    calc.close();
    
    
    return 0;
}

10 * 3 = 30
10 / 3 = 10 % 3 = 1
10 % 3 = .....Invalid mathematical operator.
10 + 3 = 13
10 / 0 = infinity as denominator is zero
10 - 3 = 7
10 ! 5 = .....Invalid mathematical operator.
10 * 10 = 100
Program ended with exit code: 0

Hint:

1. use more whitespace in writing your code. Clearly laying out the code makes debugging a lot quicker and easier.

2. Avoid duplicating all the messaging.

3. A switch control is ideal for this job.

4. Note the use of while loop.

[48T7M4Gy]

Just for interest to demonstrate:

#include <iostream>
#include <fstream>

void print_result(int, int, char, int);

int main() {
    
    int first = 0, second = 0;
    char mathOperation;
    
    std::ifstream calc;
    calc.open ("calc.txt");
    while( calc >> first >> second >> mathOperation)
    {
        switch (mathOperation){
            case '*':
                print_result(first, second, mathOperation, first * second);
                break;
                
            case '/':
                if( second == 0 ){
                    std::cout
                    << first << ' ' << mathOperation << ' ' << second
                    << "  *** Division by zero\n";
                }
                else
                    print_result(first, second, mathOperation, first / second);
                break;
                
            case '+':
                print_result(first, second, mathOperation, first + second);
                break;
                
            case '-':
                print_result(first, second, mathOperation, first - second);
                break;
                
            default:
                std::cout
                << first << ' ' << mathOperation << ' ' << second
                << " *** Operator unknown\n";
        }
    }
    
    calc.close();
    return 0;
}

void print_result(int aFirst, int aSecond, char aOperation, int aAnswer)
{
    std::cout
    << aFirst << ' ' << aOperation << ' ' << aSecond << " = " << aAnswer << '\n';
}

10 * 3 = 30
10 / 3 = 3
10 % 3 *** Operator unknown
10 + 3 = 13
10 / 0  *** Division by zero
10 - 3 = 7
10 ! 5 *** Operator unknown
10 * 10 = 100
Program ended with exit code: 0

[XxLooneyTunes]

Okay I understand what I was doing wrong now, thanks guys!!