編程訓練——進制轉換

題目

編制函數Itob(int n, char s[], int b)，將整數n轉化爲b進製表示形式，結果存入數組s中，
b的取值範圍是2，8，16，s的最大長度爲100.

思路就是現將整數轉換爲二進制數，然後將二進制數轉換爲8進制和16進制。沒有什麼難度，考研的是基礎和細緻度。

代碼

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

#define maxl 105

void reversed(char s[]){
    char temp;
    int len = strlen(s);
    for(int i = 0;i < len/2;i++){
        temp = s[len-1-i];
        s[len-1-i] = s[i];
        s[i] = temp;
    }

}

void Itob(int n, char s[], int b){

    // 先將n轉換爲二進制，結果倒序存入數組備用
    char res[maxl];
    int temp, cur, len;
    cur = 0;
    while(n/2!=0){
        res[cur++] = n % 2 + '0';
        n /= 2;
    }
    res[cur++] = '1';
    res[cur] = '\0';
    cur = 0;
    len = strlen(res);

    // 轉二進制
    if(b==2){
        for(int i = 0;i < len;i++){
            s[i] = res[i];
        }
        s[len] = '\0';
        reversed(s);
    }

    // 轉八進制
    if(b==8){
        int loop_count = len / 3;
        int remain = len % 3;
        for(int i = 1;i <= loop_count;i++){
            temp = (res[(i-1)*3]-'0')*1+(res[(i-1)*3+1]-'0')*2
                    +(res[(i-1)*3+2]-'0')*4;
            s[cur++] = temp + '0';
            temp = 0;
        }
        if(remain==0){
            s[cur] = '\0';
            reversed(s);
        }
        else if(remain==1){
            s[cur++] = 1 + '0';
            s[cur] = '\0';
            reversed(s);
        }
        else if(remain==2){
            s[cur++] = 2 + (res[len-2]-'0') + '0';
            s[cur] = '\0';
            reversed(s);
        }
    }

    // 轉十六進制
    if(b==16){
        int loop_count = len / 4;
        int remain = len % 4;
        for(int i = 1;i <= loop_count;i++){
            temp = (res[(i-1)*4]-'0')*1+(res[(i-1)*4+1]-'0')*2
                    +(res[(i-1)*4+2]-'0')*4+(res[(i-1)*4+3]-'0')*8;
            if(temp<10){
                s[cur++] = temp + '0';
            }
            else{
                s[cur++] = 'A' + temp - 10;
            }
            temp = 0;
        }
        if(remain==0){
            s[cur] = '\0';
            reversed(s);
        }
        else if(remain==1){
            s[cur++] = 1 + '0';
            s[cur] = '\0';
            reversed(s);
        }
        else if(remain==2){
            s[cur++] = 2 + (res[len-2]-'0') + '0';
            s[cur] = '\0';
            reversed(s);
        }
        else if(remain==3){
            s[cur++] = 4 + (res[len-2]-'0') * 2 + (res[len-3]-'0') + '0';
            s[cur] = '\0';
            reversed(s);
        }
    }
}

int main(){
    char s[maxl];
    int n, b;
    while(scanf("%d %d", &n, &b)==2){
        Itob(n, s, b);
        printf("%s\n", s);
    }

    return 0;
}