C程序收银系统

Question

嗯，我才学C编程2个月。我这里拿到的代码是为了解决一个收银系统。我得到了一些条形码编号、商品名称和价格。收银员输入多个条形码并按 F 结束后，应显示带有商品编号、代码和价格的收据。这些是我编译的代码。但是，我只能输入一个条码，程序就崩溃了。

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

int main()
{
typedef struct goods
{
    char goods_code[6];
    char goods_descrip[20];
    float price;
}goodtype;

goodtype goods[13];
strcpy(goods[0].goods_descrip, "Chicken");
strcpy(goods[0].goods_code, "00310");
goods[0].price = 35.00;

strcpy(goods[1].goods_descrip, "Pork");
strcpy(goods[1].goods_code, "00311");
goods[1].price = 20.50;

strcpy(goods[2].goods_descrip, "Beef");
strcpy(goods[2].goods_code, "00322");
goods[2].price = 45.00;

strcpy(goods[3].goods_descrip, "Fish");
strcpy(goods[3].goods_code, "00323");
goods[3].price = 40.00;

strcpy(goods[4].goods_descrip, "Walmart T Shirt");
strcpy(goods[4].goods_code, "00510");
goods[4].price = 75.00;

strcpy(goods[5].goods_descrip, "Walmart Trousers");
strcpy(goods[5].goods_code, "00511");
goods[5].price = 120.00;

strcpy(goods[6].goods_descrip, "Walmart Coat");
strcpy(goods[6].goods_code, "00512");
goods[6].price = 100.00;

strcpy(goods[7].goods_descrip, "Walmart Jumper");
strcpy(goods[7].goods_code, "00513");
goods[7].price = 85.00;

strcpy(goods[8].goods_descrip, "Mug");
strcpy(goods[8].goods_code, "00710");
goods[8].price = 15.50;

strcpy(goods[9].goods_descrip, "Fry Pan");
strcpy(goods[9].goods_code, "00711");
goods[9].price = 200.00;

strcpy(goods[10].goods_descrip, "Bowl");
strcpy(goods[10].goods_code, "00712");
goods[10].price = 25.00;

strcpy(goods[11].goods_descrip, "Dish");
strcpy(goods[11].goods_code, "00713");
goods[11].price = 25.00;

char tempCode[6];
char receiptNM[20], receiptCD[6];
char stop[2] = {"F"};
float receiptPC, ttlcost = 0;
unsigned int i;

printf("Please enter the item code. Type F to finish");
scanf("%s", &tempCode);

while ( strcmp(tempCode, stop) ){
    for (i = 0; i <= 12; ++i){
        if (strcmp(tempCode, goods[i].goods_code) == 0){
            strcpy(receiptNM, goods[i].goods_descrip);
            strcpy(receiptCD, goods[i].goods_code);
            receiptPC = goods[i].price;
            ttlcost += goods[i].price;
        }
        else{
            printf("This item code does not exist! Try again!\n");
    }
printf("Please enter the item code. Type F to finish");
scanf("%s", &tempCode);
}
printf("_____________________________________\n\n");
printf("      THANK YOU FOR VISITING US!     \n");
printf("_____________________________________\n");
printf("         Here is your receipt:       \n\n");
printf("%10s%20s%10s", "Item", "Code", "Price");
printf("%10s%20s%10.2f\n", receiptNM, receiptCD, receiptPC);
printf("\n_____________________________________\n");
printf("          TOTAL COST:%.2f            \n", ttlcost);
}

我为此苦苦挣扎了几个小时，无法解决。示例输出应该是Sample receipt

当我键入00310时，程序无法识别它。当我输入 310 时，它可以。

此外，当输入的代码不存在时，错误消息应该只显示一次。但是在我的程序中，它执行了 12 次。

Answer 1

这里

for (i = 0; i <= 12; ++i){
    if (strcmp(tempCode, goods[i].goods_code) == 0){

您正在访问上次迭代中未初始化的值（未定义的行为），因为您刚刚从 goods[0] 填充到 goods[11]:

strcpy(goods[11].goods_descrip, "Dish");
strcpy(goods[11].goods_code, "00713");
goods[11].price = 25.00;

Answer 2

你犯了几个错误。让我指出他们：- Keine Lust 指出的第一个：，您通过迭代到 12（含）来访问超出数组范围的内存。如果您声明了一个包含 12 个元素的数组，则索引范围为 0 到 11 而不是 0 到 12

for (i = 0; i <= 12; ++i){  //wrong iterations (< 12 should be here)
    if (strcmp(tempCode, goods[i].goods_code) == 0) {
        strcpy(receiptNM, goods[i].goods_descrip);
        strcpy(receiptCD, goods[i].goods_code);
        receiptPC = goods[i].price;
        ttlcost += goods[i].price;
    }
    else {
        printf("This item code does not exist! Try again!\n");
    }
    printf("Please enter the item code. Type F to finish");
    scanf("%s", &tempCode);
}

您的程序肯定会打印 "This item code doesn't exist!..." 12 次，因为 else 部分与 if 相关联并嵌套在 for 循环中。因此，在循环的 12 次迭代中，每次找不到项目时都会调用它。

正确的程序是：-

----   //Rest above is same
unsigned int i;
printf("Please enter the item code. Type F to finish");
scanf("%s", tempCode);

while ( strcmp(tempCode, stop) ) {
    for (i = 0; i < 12; ++i){
        if (strcmp(tempCode, goods[i].goods_code) == 0){
            strcpy(receiptNM, goods[i].goods_descrip);
            strcpy(receiptCD, goods[i].goods_code);
            receiptPC = goods[i].price;
            ttlcost += goods[i].price;
            break;
        }
    }
    if (i==12)   //The loop iteration is complete, and i becomes 12 only when the for above hasn't been breaked (same as item found)
        printf("This item code does not exist! Try again!\n");
    printf("Please enter the item code. Type F to finish");
    memset(tempCode,'[=11=]',sizeof(tempCode));
    scanf("%s", tempCode);
}

你在最后的收据部分也有错误：-

printf("%10s%20s%10s", "Item", "Code", "Price");
printf("%10s%20s%10.2f\n", receiptNM, receiptCD, receiptPC); //receiptNM, receiptCD and receiptPC are only single character arrays.

与您的预期不同，它们将只存储一个字符串。为了存储所有这些，您创建了一个结构数组（包含项目代码、项目名称和价格）。按照 GumBoy 的回答：-

Answer 3

正在查看您的输出图像。您将需要一个 for 循环来打印出这些值。在您当前的程序中，每次满足 if 语句中的条件时，都会替换 receiptCD、reciptNM 和 recieptPC 的值。我认为您需要为收据添加另一个 typedef 结构。

我解决了一些问题，但你几乎已经解决了。最后一件事是文本的合理性。

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

int main()
{
typedef struct goods
{
char goods_code[6];
char goods_descrip[20];
float price;
}goodtype;

goodtype goods[13];
strcpy(goods[0].goods_descrip, "Chicken");
strcpy(goods[0].goods_code, "00310");
goods[0].price = 35.00;

strcpy(goods[1].goods_descrip, "Pork");
strcpy(goods[1].goods_code, "00311");
goods[1].price = 20.50;

strcpy(goods[2].goods_descrip, "Beef");
strcpy(goods[2].goods_code, "00322");
goods[2].price = 45.00;

strcpy(goods[3].goods_descrip, "Fish");
strcpy(goods[3].goods_code, "00323");
goods[3].price = 40.00;

strcpy(goods[4].goods_descrip, "Walmart T Shirt");
strcpy(goods[4].goods_code, "00510");
goods[4].price = 75.00;

strcpy(goods[5].goods_descrip, "Walmart Trousers");
strcpy(goods[5].goods_code, "00511");
goods[5].price = 120.00;

strcpy(goods[6].goods_descrip, "Walmart Coat");
strcpy(goods[6].goods_code, "00512");
goods[6].price = 100.00;

strcpy(goods[7].goods_descrip, "Walmart Jumper");
strcpy(goods[7].goods_code, "00513");
goods[7].price = 85.00;

strcpy(goods[8].goods_descrip, "Mug");
strcpy(goods[8].goods_code, "00710");
goods[8].price = 15.50;

strcpy(goods[9].goods_descrip, "Fry Pan");
strcpy(goods[9].goods_code, "00711");
goods[9].price = 200.00;

strcpy(goods[10].goods_descrip, "Bowl");
strcpy(goods[10].goods_code, "00712");
goods[10].price = 25.00;

strcpy(goods[11].goods_descrip, "Dish");
strcpy(goods[11].goods_code, "00713");
goods[11].price = 25.00;

char tempCode[6];
typedef struct receipt
{
char receiptNM[20], receiptCD[6];
float receiptPC;
}receipttype;
receipttype receipt[13];
char stop[2] = {"F"};
float ttlcost = 0;
unsigned int i;
unsigned int count = 0;



while ( strcmp(tempCode, stop) ){
printf("Please enter the item code. Type F to finish: ");
scanf("%s", tempCode);
for (i = 0; i <= 12; ++i){
    if (strcmp(tempCode, goods[i].goods_code) == 0){
        strcpy(receipt[count].receiptNM, goods[i].goods_descrip);
        strcpy(receipt[count].receiptCD, goods[i].goods_code);
        receipt[count].receiptPC = goods[i].price;
        ttlcost += goods[i].price;
        count++;
    }

}

}
printf("_____________________________________\n\n");
printf("      THANK YOU FOR VISITING US!     \n");
printf("_____________________________________\n");
printf("         Here is your receipt:       \n\n");
printf("%10s%20s%10s", "Item", "Code", "Price\n");
for (int j= 0; j < count; ++j){
printf("%10s%20s%10.2f\n", receipt[j].receiptNM, receipt[j].receiptCD, receipt[j].receiptPC);
}
printf("\n_____________________________________\n");
printf("          TOTAL COST:%.2f            \n", ttlcost);
}

Answer 4

由于没有其他人提到它，这里有一个更好的方法来填充结构数组。

typedef struct
{
    char  *code;
    char  *description;
    float price;
}goodtype;

static goodtype goods[] =
{
    { "00310", "Chicken" ,  35.00 },
    { "00311", "Pork"    ,  20.50 },
    { "00322", "Beef"    ,  45.00 },
    { "00323", "Fish"    ,  40.00 },
    { "00510", "T Shirt" ,  75.00 },
    { "00511", "Trousers", 120.00 },
    { "00512", "Coat"    , 100.00 },
    { "00513", "Jumper"  ,  85.00 },
    { "00710", "Mug"     ,  15.50 },
    { "00711", "Fry Pan" , 200.00 },
    { "00712", "Bowl"    ,  25.00 },
    { "00713", "Dish"    ,  25.00 }
};
static int goodscount = sizeof(goods) / sizeof(goods[0]);

int main( void )
{
    for ( int i = 0; i < goodscount; i++ )
        printf( "%3d %s %s\n", i, goods[i].code, goods[i].description );
    printf( "Number of items: %d\n", goodscount );
}

这样做有几个好处：

输入更少，减少了人为错误的机会
节省一点内存，因为您不需要猜测 code 和 description 数组需要多大。
避免缓冲区溢出的可能性（例如，如果您猜错了字符串的长度）。
节省一点时间，因为您不需要做所有这些 strcpy。
自动计算数组中的条目数，因此您不会弄错。

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