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我对C相当陌生，我试图理解使用字符串并strcmp比较if语句中的两个字符串。

我的目标是能够根据用户输入的内容运行不同的功能。

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

void gasbill();
void electricitybill();

int main()
{
  char input[20];
  const char gasCheck[4] = "gas";
  const char electricityCheck[13] = "electricity";

  printf("Your bills explained!\n\n");
  printf("In this application I will go through your gas and electricty bills.\n");
  printf("I will explain how each of the billing payments work, \nand the calculations that go on,\n");
  printf("to create your bill.\n\n");
  printf("Please choose a bill to get started with:\n- gas\n- electricity\n\n");
  fgets(input, 20, stdin);

  if (strcmp (input, gasCheck)== 0){
    printf("\nPreparing to run Gas bill!\n\n");
    system("PAUSE");
    system("cls");
    gasbill();
    system("PAUSE");
  }
  else if (strcmp (input, electricityCheck)== 0){
    printf("\nPreparing to run Electricity bill!\n\n");
    system("cls");
    electricitybill();
    system("PAUSE");}
  else {
    printf("\nError exiting...\n\n");
    system("PAUSE");
  }

  return 0;
}

void gasbill()
{
  float balanceBroughtForward, gasThisQuarter, subTotalPerQuarter;
  char poundSign = 156;

  printf("******Your gas bill, explained!******\n\n\n");
  printf("Hello, and welcome to your gas bill, explained. Let's get started.\n");
  printf("Please enter the balance brought forward from your previous statement: \n\n%c", poundSign);
  scanf("%f", &balanceBroughtForward);
  printf("\nHow this works:\n- The money that you did not pay last quarter for your gas bill\nhas been added to this quarterly payment\n\n");
  printf("\nNext let's add this to the amount of gas you have spent this quarter. \n(how much gas have you used so far in this billing period?)");
  printf(": %c", poundSign);
  scanf("%f", &gasThisQuarter);
  printf("\n\nNow what? The two values that you have entered\n(balance brought forward 
  and gas spent this quarter)\nare added together, %c%3.2f + %c%3.2f\n", poundSign, 
  balanceBroughtForward, poundSign, gasThisQuarter);
  subTotalPerQuarter = (balanceBroughtForward + gasThisQuarter);
  printf("This is"); 
}

void electricitybill()
{
  printf("Empty");
  system("PAUSE");   
}

当它运行 if 语句时，它总是执行 gasBill 函数而不是electricalBill 函数。

提前致谢。

4

2 回答 2

5

fgets将返回一个以换行符 ( ) 结尾的字符串\n。从它的文档

从流中读取字符并将它们作为 C 字符串存储到 str 中，直到读取 (num-1) 个字符或到达换行符或文件结尾，以先发生者为准。

您可以测试尾随换行符并将其剥离

fgets(input, 20, stdin);
size_t len = strlen(input);
if (input[len-1] == '\n') {
    input[len-1] = '\0';
}

或改为使用scanf读取用户输入。

scanf("%19s", input);

作为旁白

const char gasCheck[4] = "gas";
const char electricityCheck[13] = "electricity";

可以更容易和安全地声明为

const char *gasCheck = "gas";
const char *electricityCheck = "electricity";

（这种形式可以避免将字符串文字复制到堆栈变量中。更重要的是，如果您硬编码数组的长度太小，它会消除潜在的错误来源。）

于 2013-05-15T12:44:40.620 回答
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fgets() 从标准输入读取字符，直到看到换行符或 EOF，如果看到换行符，它将存储在数组中。无论如何，fgets() 将空字符附加到数组。

所以如果你想用换行符结束你的输入，我的小改动就在这里，改变这个

const char gasCheck[4] = "gas";
const char electricityCheck[13] = "electricity";

至

const char gasCheck[5] = "gas\n";
const char electricityCheck[14] = "electricity\n";
于 2013-05-15T13:31:53.077 回答