C program to implement Top down parser with backtracking.

Grammer Rule: 
S->cAd
A->ab|a
a 
 

#include
#include

void check(void);
void set_value_backtracking(void);
void get_value_backtracking(void);
void display_output_string(void);

int iptr=0,optr=0,current_optr=0;
char output_string[20],current_output_string[20],input_string[20],temp_string[20];

int main(){
printf("\nEnter the string to check: ");
scanf("%s",input_string);
check();
return 0;}

void check(void){

   int flag=1,rule2_index=1;
    strcpy(output_string,"S");

    printf("\nThe output string in different stages are:\n");

    while(iptr<=strlen(input_string)){

        if(strcmp(output_string,temp_string)!=0){
            display_output_string();}

        if((iptr!=strlen(input_string)) || (optr!=strlen(output_string))){
            if(input_string[iptr]==output_string[optr]){
                iptr=iptr+1;
                optr=optr+1;}

            else{
                if(output_string[optr]=='S'){
                    memset(output_string,0,strlen(output_string));
                    strcpy(output_string,"cAd");}


                else if(output_string[optr]=='A'){
                    set_value_backtracking();

                    if(rule2_index==1){
                    memset(output_string,0,strlen(output_string));
                    strcpy(output_string,"cabd");}
                   

                    else{
                    memset(output_string,0,strlen(output_string));
                    strcpy(output_string,"cad");}}

                else if(output_string[optr]=='b' && input_string[iptr]=='d'){
                    rule2_index=2;
                    get_value_backtracking();
                    iptr=iptr-1;}
                   
                else{
                    printf("\nThe given string, '%s' is invalid.\n\n",input_string);
                    break;}}}

        else{
            printf("\nThe given string, '%s' is valid.\n\n",input_string);
            break;}}}
           

void set_value_backtracking(void){ //setting values for backtracking
    current_optr=optr;
    strcpy(current_output_string,output_string);
    return;}

void get_value_backtracking(void){ //backtracking and obtaining previous values
    optr=current_optr;
    memset(output_string,0,strlen(output_string));
    strcpy(output_string,current_output_string);
    return;}

void display_output_string(void){
    printf("%s\n",output_string);
    memset(temp_string,0,strlen(temp_string));
    strcpy(temp_string,output_string);
    return;}

Output: