Write the program first:

#include <stdio.h>

int main()
{
  int a = 1;
  int b = 2;
  int c = a + b;
  printf("sum is %d\n", c);

  return 0;
}

Operation results:

sum is 3

Program analysis:

Define an integer variable, a, and assign 1 to a. Define another integer variable, b, and assign 2 to b. Finally, we define an integer variable c, whose value is not assigned by assignment, but assigned to it after adding a and b, that is, the value of c is 3.