Mikro Basic Emulator for Modern PCs - version Alpha 14 by Jan Mleczko "Manna5" (CC-BY-SA license)

mikrobasic.c

#include <stdio.h>
#include <string.h>
#include <dos.h>


unsigned int variables[25];
int for_loop_begin[25];
int for_loop_max_value[25];
int program_counter;
char program_memory[20][256];
char ready_msg=1;
char continue_running=0;
char additional_newline=1;

void basic_save(){
	FILE* fp;
	fp=fopen("CASSETTE.DAT","wb");
	fwrite(program_memory,256,20,fp);
	fclose(fp);
}

void basic_load(){
	FILE* fp;
	fp=fopen("CASSETTE.DAT","rb");
	fread(program_memory,256,20,fp);
	fclose(fp);
}

void basic_new(){
	int i,j;
	for(i=0;i<20;i++){
		for(j=0;j<256;j++){
			program_memory[i][j]=0;
		}
	}
}

unsigned int basic_eval(char* expr){
	if(!strlen(expr)){
		return 0;
	}if(*expr>='0' && *expr<='9'){
		return atoi(expr);
	}else if(*expr>='A' && *expr<='Z'){
		if(strlen(expr)<2){
			return variables[*expr-65];
		}else{
			if(*(expr+1)=='+'){
				return variables[*expr-65]+basic_eval(expr+2);
			}else if(*(expr+1)=='-'){
				return variables[*expr-65]-basic_eval(expr+2);
			}else if(*(expr+1)=='*'){
				return variables[*expr-65]*basic_eval(expr+2);
			}else if(*(expr+1)=='/'){
				return variables[*expr-65]/basic_eval(expr+2);
			}
		}
	}
}

void basic_execute(char* command){
	if(*command==' '){
		basic_execute(command+1);
	}else if(!strlen(command)){
	}else{
		int i;
		char input_buffer[256]={0};
		if(!strncmp(command,"PRINT ",6) && strlen(command)>6){
			printf("      %d\n",basic_eval(command+6));
		}else if(!strncmp(command,"LET ",4) && *(command+5)=='=' && strlen(command)>6){
			variables[*(command+4)-65]=basic_eval(command+6);
		}else if(!strcmp(command,"CLS")){
			system("CLS");
		}else if(!strncmp(command,"IF ",3)){
			int enable_if=0;
			if(*(command+4)=='='){
				enable_if=variables[*(command+3)-65]==basic_eval(command+5);
			}else if(*(command+4)=='<'){
				enable_if=variables[*(command+3)-65]<basic_eval(command+5);
			}else if(*(command+4)=='>'){
				enable_if=variables[*(command+3)-65]>basic_eval(command+5);
			}
			if(enable_if){
				basic_execute(strchr(command+4,' '));
			}
		}else if(!strcmp(command,"LIST")){
			for(i=0;i<20;i++){
				if(strlen(program_memory[i])){
					printf("  %d0 %s\n",i+1,program_memory[i]);
				}
			}
			additional_newline=0;
		}else if(!strcmp(command,"NEW")){
			basic_new();
		}else if(*(command+1)=='0' && *(command+2)==' ' && *command>='1' && *command<='9'){
			strcpy(program_memory[*command-49],command+3);
			ready_msg=0;
		}else if(*(command+2)=='0' && *(command+3)==' ' && *command>='1' && *command<='9' && *(command+1)>='0' && *(command+1)<='9'){
			strcpy(program_memory[atoi(command)/10-1],command+4);
			ready_msg=0;
		}else if(!strncmp(command,"GOTO ",5) && strlen(command)>6){
			continue_running=1;
			for(program_counter=(atoi(command+5)/10)-1;program_counter<20&&continue_running;program_counter++){
				basic_execute(program_memory[program_counter]);
			}
			continue_running=0;
		}else if(!strcmp(command,"RUN")){
			basic_execute("GOTO 10");
		}else if(!strncmp(command,"INPUT ",6) && strlen(command)==7){
			printf("%c:",*(command+6));
			gets(input_buffer);
			variables[*(command+6)-65]=atoi(input_buffer);
		}else if(!strncmp(command,"FOR ",4) && *(command+5)=='='){
			variables[*(command+4)-65]=basic_eval(command+6);
			variables[1]=for_loop_max_value[*(command+4)-65]=basic_eval(strchr(command+5,' ')+4);
			for_loop_begin[*(command+4)-65]=program_counter+1;
		}else if(!strncmp(command,"NEXT ",5) && strlen(command)==6){
			char simulated_goto[]="GOTO ?00";
			if(for_loop_begin[*(command+5)-65]<10){
				simulated_goto[5]=49+for_loop_begin[*(command+5)-65];
				simulated_goto[7]=0;
			}else{
				simulated_goto[6]=48+((for_loop_begin[*(command+5)-65]+1)%10);
				simulated_goto[5]=48+((for_loop_begin[*(command+5)-65]+1)/10);
			}
			if(variables[*(command+5)-65]<for_loop_max_value[*(command+5)-65]){
				variables[*(command+5)-65]++;
				basic_execute(simulated_goto);
			}
		}else if(!strcmp(command,"EXIT")){
			exit(0);
		}else if(!strcmp(command,"SAVE")){
			basic_save();
		}else if(!strcmp(command,"LOAD")){
			basic_load();
		}else{
			puts("WHAT?\a");
			continue_running=0;
		}
	}
}

int main(){
	puts("MIKRO BASIC");
	additional_newline=0;
	char command[256]={0};
	basic_new();
	while(1){
		if(ready_msg){
			if(additional_newline){
				putchar('\n');
			}else additional_newline=1;
			puts("READY");
		}else ready_msg=1;
		putchar('>');
		gets(command);
		if(strlen(command)){
			basic_execute(command);
		}
	}
	return 0;
}