Reading two numbers – C/C++/C#
A common issue in competitive programming is reading two numbers before solve the main problem. In several programming languages this is an easy task, but we need to pay attention to some points.
In built-in C# libraries, we haven’t a method like scanffrom C/C++. This could be tricky whether you don’t know about string manipulation.
First, let’s see how to read two numbers in C language. Let the following problem.
1. Problem
Make a program that reads an integer TC as number of test cases, and in the next line, two integers, A and B. Calculate and print the sum of A and B.
1.1. Constraints
1.2. Sample Input
2
-3 5
0 110
1.3. Sample Output
2
110
2. Simple solution in C
#include<stdio.h>
int main() {
int TC, A, B;
scanf("%d", &TC);
while (TC--) {
scanf("%d %d", &A, &B);
printf("%d\n", A + B);
}
return 0;
}Note that we use scanf to read the separated numbers. That was a piece of cake, thanks to scanf.
3. Simple solution in C++
Let’s see the solution in C++ using iostream(easy way).
#include <iostream>
using namespace std;
int main(){
int TC, A, B;
cin >> TC;
while(TC--)
{
cin >> A >> B;
cout << A + B << endl;
}
cout << flush;
return 0;
}Of course, we can use scanfin both, C and C++, languages. What about C#?
4. C# approach I - using Split + Convert
static void DoFirstSolution() // Using Split and Convert
{
int TC, A, B;
string input_nextLine;
TC = Convert.ToInt32(Console.ReadLine());
while (TC > 0)
{
input_nextLine = Console.ReadLine();
A = Convert.ToInt32(input_nextLine.Split(' ')[0]);
B = Convert.ToInt32(input_nextLine.Split(' ')[1]);
Console.WriteLine(A + B);
TC--;
}
}Commonly, in C# we use ReadLinemethod to read an input from the console. In this way, input is treated as a string data type. Therefore, we need to split data to get the numbers of the sum only (and not the blank space between them). Let’s take a look at another possible solution.
5. C# approach II - using Split + Parse
static void DoSecondSolution() // Using Split + Parse
{
int TC, A, B;
string[] input_nextLine;
TC = Convert.ToInt32(Console.ReadLine());
while (TC > 0)
{
input_nextLine = Console.ReadLine().Split();
A = int.Parse(input_nextLine[0]);
B = int.Parse(input_nextLine[1]);
Console.WriteLine(A + B);
TC--;
}
}Parsecan be faster, but it's less secure than Convert(previous approach). Note the way we split data in this example (fairly different than approach I).
6. C# approach III - using LINQ
static void DoThirdSolution() // Using LINQ
{
int TC, A, B;
IEnumerable<int> input_nextLine = null;
TC = Convert.ToInt32(Console.ReadLine());
while (TC > 0)
{
input_nextLine = Console
.ReadLine()
.Split()
.Select(int.Parse);
A = input_nextLine.ToList()[0];
B = input_nextLine.ToList()[1];
Console.WriteLine(A + B);
TC--;
}
}With LINQ we can read the line, split the input data, and select the value to parse. Note the use of the IEnumerableinterface. A very convenient way to solution.
7. C# approach IV - using LINQ and regular expressions (regex)
static void DoFourthSolution() // Using LINQ + Regex
{
int TC, A, B;
TC = Convert.ToInt32(Console.ReadLine());
while (TC > 0)
{
var numbers = from Match number in new Regex(@"\d+").Matches(Console.ReadLine())
select int.Parse(number.Value);
A = numbers.ToList()[0];
B = numbers.ToList()[1];
Console.WriteLine(A + B);
TC--;
}
}Despite of this approach hasn't use IEnumerableinterface, we was able to use a "select-from" way (via LINQ) to search the numbers in the input, parse, and sum them.
8. C# approach V - using input arguments
static void Main(string[] args) // Using input args
{
int TC = Convert.ToInt32(args[0]);
int argsCount = 1;
while(TC > 0)
{
int A = Convert.ToInt32(args[argsCount]);
int B = Convert.ToInt32(args[argsCount + 1]);
Console.WriteLine(A + B);
argsCount+=2;
TC--;
}
}In this example, we use the "Main method approach". Here, we've configured the initial string arguments before run the program. To configure args in Visual Studio, follow those steps:
Open
Project Settings (right click on your project name)>Debug, and setCommand Line Arguments. Example: 2 100 -3 85 91.Save, build and run your project.
9. Conclusion
There are several ways to read numbers using C#. But, in contrast of C and C++, in C#, the built-in libraries treat input numbers as string. Nevertheless, C# has powerful components, like LINQ, that make the life of programmer easier.
10. References
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