写在前面

  • 实现思路
  • 字符数组存储输入数字
  • 通过​​sscanf​​​、​​sprintf​​ 处理读取字符串
  • ​​cstdio​​头文件下
  • ​​sscanf(a, "%lf", &real_num);​​​ : 将字符数组str中的内容以​​%lf​​​格式写到​​real_num​​中（从左至右）
  • ​​sprintf(b, "%.2f",real_num);​​​ : 把​​real_num​​​以​​%.2f​​形式写到str字符数组中
  • 字符循环对比、浮点数范围判断
  • 题目较为简单，熟识​​sscanf / sprintf​​函数事半功倍。
  • 15分钟内可a题

测试用例

input:
7
5 -3.2 aaa 9999 2.3.4 7.123 2.35
output:
ERROR: aaa is not a legal number
ERROR: 9999 is not a legal number
ERROR: 2.3.4 is not a legal number
ERROR: 7.123 is not a legal number
The average of 3 numbers is 1.38

input:
2
aaa -9999
output:
ERROR: aaa is not a legal number
ERROR: -9999 is not a legal number
The average of 0

ac代码

#include <iostream>
#include <cstdio>
#include <string.h>
using namespace std;
int main() {
    int n, cnt = 0;
    char a[50], b[50];
    double real_num = 0.0,  sum = 0.0;

    scanf("%d", &n);
    for(int i = 0; i < n; i++) {
        scanf("%s", a);
        sscanf(a, "%lf", &real_num);
        sprintf(b, "%.2f",real_num);

        int flag = 0;
        for(int j = 0; j < strlen(a); j++)
            if(a[j] != b[j]) flag = 1;
        if(flag || real_num < -1000 || real_num > 1000) {
            printf("ERROR: %s is not a legal number\n", a);
            continue;
        } else {
            sum += real_num;
            cnt++;
        }
    }
    if(cnt == 1)
        printf("The average of 1 number is %.2f", sum); 
    else if(cnt > 1)
        printf("The average of %d numbers is %.2f", cnt, sum / cnt);
    else
        printf("The average of 0 numbers is Undefined");
    return 0;
}

知识点小结

  • sprintf、sscanf函数熟练使用
// Write formatted data to string
int sprintf ( char * str, const char * format, ... );

// Read formatted data from string
int sscanf ( char * str, const char * format, ...);
  • ​​sprintf​​简单示例
/* sprintf example */
#include <stdio.h>

int main ()
{
  char buffer [50];
  int n, a=5, b=3;
  n=sprintf (buffer, "%d plus %d is %d", a, b, a+b);
  printf ("[%s] is a %d char long string\n",buffer,n);
  return 0;
}
Output:
[5 plus 3 is 8] is a 13 char long
  • ​​sscanf​​简单示例
/* sscanf example */
#include <stdio.h>

int main ()
{
  char sentence []="Rudolph is 12 years old";
  char str [20];
  int i;

  sscanf (sentence,"%s %*s %d",str,&i);
  printf ("%s -> %d\n",str,i);
  
  return 0;
}
Output:
Rudolph -> 12