B1054 求平均值 (20 分 | 字符串处理，附详细注释，逻辑分析)

写在前面

• 思路分析
  • 字符数组存储读入数据，char a[50], b[50];
  • 字符串格式化读取、格式化写入函数
    • sscanf() – 从1个字符串中读进与指定格式相符的数据
    • sprintf() – 字符串格式化命令，主要功能是把格式化的数据写入某个字符串
• 问题点
  • 合法区间、合法实数校验，[−1000,1000]
  • 输出坑，numbers / numbers
    • The average of K numbers is Y，其中 K 是合法输入的个数，Y 是它们的平均值，精确到小数点后 2 位
    • 如果平均值无法计算，则用 Undefined 替换 Y
    • 如果 K 为 1，则输出 The average of 1 number is Y
• 题目简单，10分钟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 numbers is Undefined

ac代码

#include <iostream>
#include <cstdio>
#include <string.h>
using namespace std;

int main()
{
    int n, cnt = 0;
    cin >> n;

    char a[50],b[50];
    double tmp, sum = 0.0;
    for(int i=0; i<n; i++)
    {
        scanf("%s", a);
        sscanf(a, "%lf", &tmp);
        sprintf(b, "%.2f", tmp);
        int flag = 0;
        for(int j=0; j<strlen(a); j++)
            if(a[j]!=b[j]) flag = 1;
        if(flag || tmp<-1000 || tmp>1000)
        {
            printf("ERROR: %s is not a legal number\n", a);
            continue;
        }
        else
        {
            sum+=tmp;
            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

• sscanf

  • 格式化字符串输入
  • int sscanf ( char * str, const char * format, ...);

  • /* 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
    

• sprintf

  • 字串格式化命令，主要功能是把格式化的数据写入某个字符串
  • int sprintf ( char * str, const char * format, ... );
    • 返回值：字符串长度（strlen）

  • /* 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 string
    

标签：20,int,number,legal,B1054,char,numbers,ERROR,字符串
来源： https://blog.csdn.net/qq_24452475/article/details/100185336