题解 | #添加逗号#

#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#include <string.h>
//1234567
//1,234,567
//765,432,1
void reverse(char* sta, char* end) {
    char c;
    while (sta < end) {
        c = *sta;
        *sta = *end;
        *end = c;
        sta++;
        end--;
    }
}
int main() {
    char arr[20] = { 0 };
    scanf("%s", arr);
    char arr2[200] = { 0 };
    // char *sta=arr;

    int cnt = 0;
    int len = strlen(arr);
    int i = len - 1;
    int j = 0;
    while (i >= 0) {
        for (j = 0; j < 3; j++) {
            if (i >= 0)
                arr2[cnt++] = arr[i--];
        }
        if (i != -1)
            arr2[cnt++] = ',';

    }
    char* sta = arr2;
    char* end = &arr2[cnt - 1];
    reverse(sta, end);
    printf("%s", arr2);
    return 0;
}