記錄——《C Primer Plus （第五版）》第八章編程練習第八題

 編寫一個程序，顯示一個菜單，爲您提供加法、減法、乘法或除法的選項。獲得您的選擇後，該程序請求兩個數，然後執行您選擇的操作。該程序應該只接受它所提供的菜單選項。它應該使用float類型的數。並且如果用戶未能輸入數字應允許其重新輸入。在出發的情況中，如果用戶輸入0作爲第二個數，該程序應該提示用戶輸入一個新的值。

# include <stdio.h>

float add(float one, float two);
float sub(float one, float two);
float mul(float one, float two);
float div(float one, float two);
float get();
//bool is_enter();    //有錯不明白

int main(void)
{
    float one;
    float two;
    char ch;

    printf("********計算器********\n\n");
    printf("a. add     s. subtract\n");
    printf("m. multiply  d. divide\n");
    printf("q. quit\n\n");
    printf("**********************\n");  
    while((ch = getchar()) != 'q')
    {
        switch(ch)
        {
        case 'a':
            one = get();
            two = get();
            printf("%.3f + %.3f = %.3f\n", one, two, add( one, two));
            break;
        case 's': 
            one = get();
            two = get();
            printf("%.3f - %.3f = %.3f\n", one, two, sub( one, two));
            break;
        case 'm':
            one = get();
            two = get();
            printf("%.3f * %.3f = %.3f\n", one, two, mul( one, two));
            break;
        case 'd':
            one = get();
            two = get();
            if(two == 0)
                two = get();
            printf("%.3f / %.3f = %.3f\n", one, two, div( one, two));
            break;


        }
    }

    return 0;
}

float get()
{
    float num;
    printf("Please enter a number :\n");
    while(scanf("%f", &num) != 1)
        printf("Please enter anther number :\n");

    return num;
}

float add(float one, float two)
{
    float sum;
    sum = one + two;
    return sum;
}

float sub(float one, float two)
{
    float sub;
    sub = one - two;
    return sub;
}

float mul(float one, float two)
{
    float mul;
    mul = one * two;
    return mul;
}

float div(float one, float two)
{
    float div;
    div = one / two;
    return div;
}