C语言编程 - 循环，直到用户输入号码scanf函数 [英] C programming - Loop until user inputs number scanf

问题描述

我需要我的程序错误检查帮助。我要求用户输入一个整数，我想检查，如果用户输入的是一个整数。如果没有，重复scanf函数。

我的code：

  INT主要（无效）{  INT数字1，数字;
  INT总和;  //要求用户整数加
  的printf（请输入第一个整​​数的补充。）;
  scanf函数（％d个，＆安培;数量1）;  的printf（请输入第二个整数补充。）;
  scanf函数（％d个，＆安培;数字2）;
  //添加整数
  总和=数字1 +数字2;  //打印总和
  的printf（，数字1，数字，总和％D和％D =％d个\\ n之和）;  //检查是否总和divisable 3
  如果（总和％3 == 0）{
    的printf（这两个整数的和是3的倍数\\ n！）;
  }其他{
    的printf（这两个整数的和是不是3的倍数... \\ n）;
  }
  返回0;
}
 

解决方案

scanf函数返回它已按照您的格式读取成功的项目数。您可以设置一个循环退出只有当 scanf函数（％d个，＆安培;数字2）; 收益 1 。这一招，但是，忽略无效数据时 scanf函数返回零，所以code是这样的：

 而（scanf函数（％d个，＆安培;！号码2）= 1）{
    //告诉该条目是无效的用户
    的printf（你没有输入有效的数字\\ n）;
    //星号*告诉scanf函数读取和忽略的价值
    scanf函数（％* S）;
}
 

由于您为code读取数超过一次，考虑一个函数来隐藏这个循环，并在主，以避免两次调用这个函数重复。

I need help with error checking for my program. I'm asking the user to input a integer and I would like to check if the users input is a integer. If not, repeat the scanf.

My code:

int main(void){

  int number1, number2;
  int sum;

  //asks user for integers to add
  printf("Please enter the first integer to add.");
  scanf("%d",&number1);

  printf("Please enter the second integer to add.");
  scanf("%d",&number2);
  //adds integers
  sum = number1 + number2;

  //prints sum
  printf("Sum of %d and %d = %d \n",number1, number2, sum);

  //checks if sum is divisable by 3
  if(sum%3 == 0){
    printf("The sum of these two integers is a multiple of 3!\n");
  }else {
    printf("The sum of these two integers is not a multiple of 3...\n");
  }
  return 0;
}

解决方案

scanf returns the count of items that it has successfully read according to your format. You can set up a loop that exits only when scanf("%d", &number2); returns 1. The trick, however, is to ignore invalid data when scanf returns zero, so the code would look like this:

while (scanf("%d",&number2) != 1) {
    // Tell the user that the entry was invalid
    printf("You did not enter a valid number\n");
    // Asterisk * tells scanf to read and ignore the value
    scanf("%*s");
}

Since you read a number more than once in your code, consider making a function to hide this loop, and call this function twice in your main to avoid duplication.

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