Multiple Inputs to a C Program through C#

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C++

C#

I am working on passing inputs to an .exe file generated by compiling a C program by Compiler through C#. My C# code is:

string line = "1" + " 2 " ;

Process p = new Process();                
p.StartInfo.CreateNoWindow = true;
p.StartInfo.WindowStyle = System.Diagnostics.ProcessWindowStyle.Hidden;
p.StartInfo.FileName = "C:\\..\\demo1.exe";
p.StartInfo.WindowStyle = ProcessWindowStyle.Hidden;
p.StartInfo.UseShellExecute = false;
p.StartInfo.RedirectStandardOutput = true;
p.StartInfo.RedirectStandardInput = true;
p.Start();
p.StandardInput.WriteLine(line);

p.Close();

I successfully passed single inputs for C programs that read one input. But when i try to pass multiple inputs to C programs requiring multiple inputs, it only run exe file and it do not read/pass any of the inputs i provide. Also i have hidden the process of exe file but it opens it.

My C Code to which am trying to pass multiple inputs is:

#include<stdio.h>

int main()
{
   int a, b, c;

   printf("Enter two numbers to add\n");
   scanf("%d%d",&a,&b);

   c = a + b;

   printf("Sum of entered numbers = %d\n",c);

   return 0;
}

Any kind of help / suggestion will be appreciated.