Lab 2: Revision on C++ (2)

# Lab 2

## Revision on C++ (2)

##### Presentation by *Asem Alaa*

<div class="my-header"><img src="/gallery/cairo.png" style="height: 30px;" /></div>
<div class="my-footer"><span>SBE201 Data Structures and Algorithms  (Spring 2020) - By <em>Asem</em></span></div>

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## Command Line Arguments

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### Examples: Why Command Line Arguments

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* `apt-get install vlc`
* `git commit -a -m "correction of problem 3!"`
* `cp [file] [target path]`

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### Command Line Arguments in C and C++

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```c++
#include <iostream>
// argc is counter for the arguments, including the application-name.
// argv is array of strings representing the arguments.
int main( int argc, char *argv[] )
{
    std::cout << "Arguments count:" << argc << std::endl;

for( int i = 0 ; i < argc ; ++i )
    {
        std::cout << "Argument:" << argv[ i ] << std::endl;
    }
}
```

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#### Example: Simple calculater from command line arguments

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What if we have a simple calculator like this.

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```terminal
$ ./myCalculator 12.4 + 3.2
20
```

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![](/gallery/argv2.svg)

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#### Convert from string form to integer form?

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```c++
int x = "40"; // Compiler Error (Type Mismatch)

int y = std::atoi("40"); // Now this works, and y = 40.

double z = std::atof("13.9"); // z = 13.9
```

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* `std::atoi` converts string representation => integer representation.
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* `std::atof` converts a string representation => double representation.
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* `#include <cstdlib>`.

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```c++
#include <iostream>
#include <cstdlib>

// Our logic
double calculation( double a , double b , char operation );

int main( int argc , char *argv[] )
{
    double a = std::atof( argv[1] );
    double b = std::atof( argv[3] );

char *op_string = argv[2];
    char op = op_string[0];

std::cout << calculcation( a , b , op ) << std::endl;
    return 0;
}
```

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```c++
double calculation( double a , double b , char operation )
{
  switch( operation )
  {
    case '+': return a + b;
    case '-': return a - b;
    case 'x': return a * b;
    case '/': return a / b;
    default:  return 0;
  }
}
```

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![](/gallery/argv2.svg)

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## Making Your Own Header Libraries

### [{DRY}](https://en.wikipedia.org/wiki/Don%27t_repeat_yourself)
#### i.e Don't repeat your self

* Don't copy codes.
* If you need to fix a mistake, fix it from one place.

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</textarea>
</cstdlib></iostream></cstdlib></iostream>