/* Homework my_printf.c
 * 2017-2 Internet Programming
 * Written by Choe Hyeong Jin, CS Dept., Univ. of Seoul
 */
#include <stdio.h> // putchar, puts
#include <stdarg.h> // 가변 인자 ... 처리
 
char *convert(unsigned int num, int base) { // 원하는 진법으로 변환해주는 함수 
    static char Representation[]= "0123456789ABCDEF";
    static char buffer[50]; // 최대 49개의 숫자 표시
    char *ptr; 
 
    ptr = &buffer[49]; 
    *ptr = '\0'; // 문자열의 끝에는 항상 '\0'을 표시
 
    do { 
        *--ptr = Representation[num%base]; 
        num /= base; 
    }while(num != 0); // 진법 변환 후 문자열로 처리
 
    return(ptr); 
}
 
void my_printf(char* format,...) { 
    char *traverse; 
    unsigned int i;
    char *s; 
 
    //1. my_printf의 인수들 초기화하기.
    va_list arg; 
    va_start(arg, format); 
 
    for(traverse = format; *traverse != '\0'; traverse++) { // 문자열의 끝이 나올 때까지 순회
        while( *traverse != '%' ) { // 형식 지정자가 나올때까지 
            putchar(*traverse); // 한글자씩 출력
            traverse++;  // 포인터 증가
        } 
 
        traverse++; // 형식 지정자 % 다음 글자 위치
 
        //2. 인수들을 가져오고 형식 지정자에 알맞게 출력하기.
        switch(*traverse) { 
            case 'c' : i = va_arg(arg,int); putchar(i); break; // 문자 인수 출력
            case 'd' : i = va_arg(arg,int); // 정수(10진수) 출력
                    	if(i<0) { // 음수일 경우
                            i = -i; putchar('-'); 
                        } 
                        puts(convert(i,10)); // 10진수로 변환 후 문자열 출력
                        break; 
            case 'o': i = va_arg(arg,unsigned int); // 8진수 출력
                        puts(convert(i,8)); // 8진수로 변환 후 문자열 출력
                        break; 
            case 's': s = va_arg(arg,char *); puts(s); break; // 문자열 출력
            case 'x': i = va_arg(arg,unsigned int); // 16진수 출력
                        puts(convert(i,16)); // 16진수로 변환 후 문자열 출력
                        break; 
        }   
    } 
 
    //3. 인수 스캔 끝.
    va_end(arg); 
} 
 
int main(){
	int i=1;
	my_printf("i is %d\n", i);
	return 0;
}

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