Why does the loop (C language) work incorrectly?

Question

C++ / C#

#include<stdio.h>
main()
{
  /*4.28*/
  int earnings, wagesperunit, wages, hourly, hours, cod, i, numberofunits;
  for(i=1;i<=5;i++){
    printf("Enter the cod of worker: ");
    cod=getchar();
    switch(cod){
        case '1':
        printf("Enter the wages for administrator: ");
        scanf("%d",&wages);
        printf("Wages is: %d\n",wages);
        break;

        case '2':
        printf("Enter the business hours: ");
        scanf("%d",&hours);
        printf("Enter the hourly: ");
        scanf("%d",&hourly);
        hourly=hourly*40;
        if(hours>=40)
          hourly=hourly+((hours-40)*1.5);
        printf("Wages is: %d\n",hourly);
        break;

        case '3':
        printf("Enter the earnings: ");
        scanf("%d",&earnings);
        earnings=earnings*0.057+250;
        printf("Wages is: %d\n", earnings);
        break;

        case '4':
        printf("Enter wages per unit: ");
        scanf("%d", &wagesperunit);
        printf("Enter number of units: ");
        scanf("%d", &numberofunits);
        wagesperunit=wagesperunit*numberofunits;
        printf("Wages is: %d\n", wagesperunit);
        break;

        case '\n': case ' ':
        break;

        default:
          printf("Incorrect letter cod. Enter a new cod.\n");
          break;
      }
  }

return 0;
}

This common exercise from Deitel's book "How to Program in C++" got me into a dead end. The iteration is somehow wrong in the loop. However, here is a screenshot of the console program.

I don’t know why, but after the first input of a value, the program starts to display messages twice asking you to enter values.

Answer 1

An extra 'Enter' remains in the buffer, then it works

case '\n': case ' ':
        break;

and you find yourself again at the invitation to enter the code.
You can make sure by adding some message before the break in this case.