如何在c编程中将用户输入与字符串进行比较

Question

我们正在尝试根据用户输入的内容执行 if 语句。例如，如果用户输入日元，那么我们希望执行 if 语句并计算到日元的转换。 在用户输入了多少加仑的气体后，我们就会计算出总成本。然后，我们想让用户选择他们想要将总成本转换成的货币。我们给了用户三个选择。如果用户输入的内容不是任何给定的选择，则允许用户再次重新输入选择。用户确实输入了 3 个选项之一，然后我们希望执行货币转换。

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <math.h>
#include <string.h>
#include <stdbool.h>

float gas_gallons;
float cost_today_gallons;
int main()
{
    char input;
    printf("Please enter the number of gallons of gasoline: ");
    scanf("%c", &input);

    while (!isdigit(input))
    {
        printf("\nYou need to enter a digit. Please enter the number of gallons of gasoline: ");
        scanf("%c", &input);
        }
    if (isdigit(input))
    {
        printf("\nThe users input was %c", input);
        gas_gallons = input - '0';
        printf("\nAs a float it is now %f", gas_gallons);

        float carbon_dioxide_pounds = gas_gallons * 19.64;
        printf("\n%.2f gallons of gasoline produces approximately %f pounds of carbon dioxide.", gas_gallons, carbon_dioxide_pounds );

        float barrels_crude_oil = gas_gallons/19.0;
        printf("\n%.2f gallons of gasoline requires %f barrels of crude oil.", gas_gallons, barrels_crude_oil);

        cost_today_gallons = gas_gallons*2.738;
        printf("\n%.2f gallons of gasoline costs a total average of %f US dollars today.", gas_gallons, cost_today_gallons);
        }

    char currency[100];
    printf("\nChoose a currency you want to see your total cost in (Euro, Pound, or Yen): ");
    scanf("%c", &currency);
    printf("\nThe currency chosen is %c", currency);

    char Yen[100];
    char Euro[100];
    char Pound[100];

    while (strcmp(currency, Yen) != 0 || strcmp(currency, Euro) != 0 || strcmp(currency, Pound) != 0)
    {
        printf("\nYou need choose one of these currencies (Euro, Pound or Yen). Please enter one: ");
        scanf("%s", &currency);
    }
    if (strcmp(currency, Yen) == 1)
    {
        float yen_total_cost = cost_today_gallons*123.07;
        printf("\n%.2f gallons of gasoline costs a total average of %f US dollars today.", gas_gallons, yen_total_cost);
    }
    if (strcmp(currency, Euro) == 1)
    {
        float euro_total_cost = cost_today_gallons*0.92;
        printf("\n%.2f gallons of gasoline costs a total average of %f US dollars today.", gas_gallons, euro_total_cost);
    }
    if (strcmp(currency, Pound) == 1)
    {
        float pound_total_cost = cost_today_gallons*0.65;
        printf("\n%.2f gallons of gasoline costs a total average of %f US dollars today.", gas_gallons, pound_total_cost);
        }
    return 0;
}

Answer 1

我可以在您的代码中看到一些问题：

1. 你应该使用scanf("%s", str)来读取一个字符串，见scanf()

2. 另外，strcmp() 在其参数相等时返回 0。

3. 并且您的代码中的char[] Yen, Euro, Pound 未初始化。