Thread: program that replaces three spaces with a tab

So for a course at University I had to write a program that replaces three spaces with a tab.
Then I had to change the to extend that it looks like machine language. We have to use go to statements and labels.

Warning the code is pretty ugly. I have added comments to make it clearer. I can understand if it's still unclear because goto statements are really ugly to read.

Code:

#include <stdio.h>

int R0 = 0;      //constant 0 
char R2 = '\t';      // constant tab
char R3 = '\n';  // constant '\n'
int R4 = 0;      //c           //char to store currently read character
int R5 = 0;      //counter    //counter variable for read input characters
int R6;           //i           //counter variable for for-loop      
int R7;           //diff        //to calculate difference for if-statements
char *R8;        //tmp_pointer //temporary pointer for array access
char *R9;        //tmp0_pointer //temporary pointer for array access
char buffer[15]; //buffer to store read input

char RA =EOF; // EOF

int main()
{
    //read characters from standard input until '\n' is detected
    INPUT_LOOP: 
R4= getchar();
R7 = R4-R3;
if(R7==R0){                     
goto END_INPUT_LOOP;
}

R8 = buffer+R5; 
*R8= R4;
        R5=R5+1;
        
          //break out of loop when buffer size is reached
      R7=R5 -14;
      if(R7 >R0){
      goto END_INPUT_LOOP;
      }
       
       //break out of programm if EOF is detected
       RA =EOF;
       RA= RA-R4;
      if(RA==0){
          goto END_INPUT_LOOP;
      }
      
     goto INPUT_LOOP;
     
     


// is equivalent to i =0 in while loop
    END_INPUT_LOOP: R6=R0;
    
OUTPUT_LOOP:
// prints out read input until buffer size is 0
R7= 14-R6;
if(R7 == R0) {
        goto  END_OUTPUT_LOOP; 
    }


R9 = buffer+R6; //buffer+i
       
     
      
      if(*(R9)==' ') goto A1; // if first input is space go to  label A1
      goto D3;                                                 
    A1: if(*(R9+1)==' ') goto A2; // if second input is space go to  label A2
        goto D3;
    A2: if(*(R9+2)==' ') goto set;  // if third input is space go to  label set
    
     goto D3;
     
     // 
        D3: 
        putchar(*R9);
        R6= R6+1; // this is the same as i++;      
     
     goto OUTPUT_LOOP;
     
     
     
     // this label is active when the three if conditions are met
          set:
         
          
          *R9= R2; // sets the first space to a tab
           

           putchar(*R9); // prints out the tab
           R6 = R6 +3;  // moves the index
           goto OUTPUT_LOOP;  
   

           
        // prints out newline and returns 0
    END_OUTPUT_LOOP:
  
    putchar(R3);

    return R0;  
}

Now this code does what i want it to. for example if the input is a a it replaces the three spaces with a tab.

However for the exercise I am only allowed to compare if statements with 0.
So I changed the code but the output is just weird.

Code:

#include <stdio.h>

int R0 = 0;      //constant 0 
char R2 = '\t';      // constant tab
char R3 = '\n';  // constant '\n'
int R4 = 0;      //c           //char to store currently read character
int R5 = 0;      //counter    //counter variable for read input characters
int R6;           //i           //counter variable for for-loop      
int R7;           //diff        //to calculate difference for if-statements
char *R8;        //tmp_pointer //temporary pointer for array access
char *R9;        //tmp0_pointer //temporary pointer for array access
char buffer[15]; //buffer to store read input

char RA =EOF; // EOF

int main()
{
    //read characters from standard input until '\n' is detected
    INPUT_LOOP: 
R4= getchar();
R7 = R4-R3;
if(R7==R0){                     
goto END_INPUT_LOOP;
}

R8 = buffer+R5; 
*R8= R4;
        R5=R5+1;
        
          //break out of loop when buffer size is reached
      R7=R5 -14;
      if(R7 >R0){
      goto END_INPUT_LOOP;
      }
       
       //break out of programm if EOF is detected
       RA =EOF;
       RA= RA-R4;
      if(RA==0){
          goto END_INPUT_LOOP;
      }
      
     goto INPUT_LOOP;
     
     


// is equivalent to i =0 in while loop
    END_INPUT_LOOP: R6=R0;
    
OUTPUT_LOOP:
// prints out read input until buffer size is 0
R7= 14-R6;
if(R7 == R0) {
        goto  END_OUTPUT_LOOP; 
    }


R9 = buffer+R6; //buffer+i
       
     char RX =' '; 
      
      *R9=*R9-RX;
      
      if(*(R9)==0) goto A1; // if first input is space go to  label A1
      goto D3;                                                 
    A1: if(*(R9+1)==0) goto A2; // if second input is space go to  label A2
        goto D3;
    A2: if(*(R9+2)==0) goto set;  // if third input is space go to  label set
    
     goto D3;
     
     // 
        D3: 
        putchar(*R9);
        R6= R6+1; // this is the same as i++;      
     
     goto OUTPUT_LOOP;
     
     
     // this label is active when the three if conditions are met
          set:
         
          
          *R9= R2; // sets the first space to a tab
           

           putchar(*R9); // prints out the tab
           R6 = R6 +3;  // moves the index
           goto OUTPUT_LOOP;  
   

           
        // prints out newline and returns 0

    END_OUTPUT_LOOP:
  
    putchar(R3);

    return R0;  
}

I have no idea why it's like this. I am a beginner at C.

I know that it's an ugly code but I have to do it for the assignment. The variable names are supposed to resemble registers.

Thank you in advance.

to change the code so that it can run in visual x toy