c - 我正在尝试制作一个可以根据用户在 C 中的选择来运行不同功能的程序

Question

我做了三个不同的函数。我正在尝试 atm 让用户选择要操作的功能。为此，我尝试使用 switch 语句。用户输入两个数字并选择对数字进行操作的函数。这是我目前的代码，它不起作用。MultbyTwo、isFirstBigger 和 addVat 是函数。

#include <stdio.h>

int multbyTwo (int a){
    return a*2;
}

int isFirstBigger (int a, int b){
    if (a<b){
    printf("1");
    }
    else {
    printf("0");
    }
}

float addVat(float a, float 20){
    return (a/100)*20;
}

int main(){


    int a,b;
    int choice;
    printf("Which Function [0:multbyTwo,1:isFirstBigger,2:addVat]:");
    scanf("%d",&choice);

    printf("a:\n");
    scanf("%f",&a);
    printf("b:\n");
    scanf("%f",&b);

    switch (choice){
        case 0: printf(multbyTwo(a));
            break;
        case 1: printf(isFirstBigger(a,b));
            break;
        case 2: printf(addVat(a));
            break;
    }

}

Answer 1

除了我在评论中提到的问题之外，您的许多 printf 调用中还缺少格式字符串。这是代码的工作版本，在我更改的地方添加了“///”注释:

#include <stdio.h>

int multbyTwo(int a) {
    return a * 2;
}

int isFirstBigger(int a, int b) {
    if (a < b) {
    //  printf("%s", "1"); /// You print the result in main!
        return 1; /// You MUST return a value!
    }
    else {
    //  printf("%s", "0"); /// You print the result in main!
        return 0; /// You MUST return a value!
    }
}

float addVat(float a, float vat) { /// Change here to allow a value of vat to be passed
    return (a / 100) * vat;        /// ... and here to use the passed value (not fixed)
}

int main() {
    int a, b;
    int choice;
    printf("Which Function [0:multbyTwo,1:isFirstBigger,2:addVat]:");
    scanf("%d", &choice);

    printf("a:\n");
    scanf("%d", &a); /// Use %d for integers - %f is for float types
    printf("b:\n");
    scanf("%d", &b); /// Use %d for integers - %f is for float types

    switch (choice) { /// each call to printf MUST have the format string as the first argument...
        case 0: printf("%d", multbyTwo(a));///
            break;
        case 1: printf("%d", isFirstBigger(a, b));///
            break;
        case 2: printf("%f", addVat((float)a, 20));/// Now, we must pass the value of "vat" to use in "addVat()"
            break;
    }
    return 0; /// It's good practice to always have this explicit "return 0" in main!
}

希望这对您有帮助! (但不得不说，还有很大的进步空间。)

请随时要求进一步澄清和/或解释。