gistfile1.txt

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <math.h>

int main(){
    while(1){
		printf("> ");
		printf("%d\n",calc_3());
		while(getchar()!='\n');
    }
    return 0;
}

int calc_3(){
	int result=calc_2();
	while(1){
		char op=getchar();
		switch(op){
		case '+':
			result+=calc_2();
			break;
		default:
			ungetc(op,stdin);
			return result;
		}
	}
}

int calc_2(){
	int result=calc_1();
	while(1){
		char op=getchar();
		switch(op){
		case '*':
			result*=calc_1();
			break;
		default:
			ungetc(op,stdin);
			return result;
		}
	}
}

int calc_1(){
	char top=getchar();
	if(top=='('){
		int result=calc_3();
		getchar();
		return result;
	}else if(isdigit(top)){
		int i;
		char buf[64];
		buf[0]=top;
		for(i=1;i<64;i++){
			buf[i]=getchar();
			if(!isdigit(buf[i])){
				ungetc(buf[i],stdin);
				buf[i]='\0';
				break;
			}
		}
		return atoi(buf);
	}
	return 0;
}