爲什麼我的代碼返回一個不正確的值？

Question

我對C非常陌生，我想弄清楚爲什麼我的代碼返回的值不正確。

int main() 
{ 


    printf("Welcome to my number generator! \n"); 
    printf("What is the first number in the range? \n"); 
    int rng1 = scanf("%d", &rng1); 
    printf("What is the second number in the range? \n"); 
    int rng2 = scanf("%d", &rng2); 
    printf("What would increment would you like to go up in? \n"); 
    int inc = scanf("%d", &inc); 

    do 
     { 
     printf("%d\n"rng1); 
     rng1 += inc; 
     } 
    while(rng1 != rng2); 
    } 
    return 0; 
    } 

從這個代碼，我希望第一範圍和第二範圍在一定數量的上升之間的號碼清單，而是我得到1.我做錯了的值？ P.S.我試圖'調試'它，發現當我用：

if(isalpha(rng1)); 
    printf("I am a String...") 
if(isdigit(rng1)) 
    printf("I am a Digit") 

它返回，「我是一個字符串...」。

謝謝！

Answer 1

你是通過調用scanf並且scanf已經將輸入值分配給變量rng1,rng2和inc，並且scanf返回成功填充的參數列表的項目數量。因此，將scanf的返回值分配給這些變量是不正確的。只需使用輸入數量的返回值即可。您應該讀取值1，因爲您只想讀取每個scanf的一個值。此外，您還可以檢查輸入值以檢測輸入值是否有效。

除此之外，我想對您的代碼進行一些修改。尤其是您的do{...}while();循環可能由於運算符!=而無限期地運行。請參閱下面的代碼中的評論。

int main() 
{ 
    /* Declare the variables and do not assign the return value of scanf */ 
    int rng1, rng2, inc; 
    printf("Welcome to my number generator! \n"); 
    printf("What is the first number in the range? \n"); 
    /* repeat this check condition for each scanf, exit(EXIT_FAILURE) requires #include <stdlib.h>*/ 

    if (1 != scanf("%d", &rng1)) { 
     exit(EXIT_FAILURE); 
    } 
    printf("What is the second number in the range? \n"); 
    scanf("%d", &rng2); 
    printf("What would increment would you like to go up in? \n"); 
    scanf("%d", &inc); 

    do 
    { 
     printf("%d\n",rng1); 
     rng1 += inc; 
    } 
    /* Use <= instead of != and think about the case for rng1 is 1 rng2 is 5 and inc is 3, can you detect the end of the loop by adding 3 to the starting point 1 ? */ 
    while(rng1 <= rng2); 

    /* Remove the `}` here */ 
    return 0; 
} 

Answer 2

當您傳遞變量的地址（使用&運算符）時，允許scanf將掃描值寫入變量。 scanf的返回值是而不是您正在查找的值（這是別的）。

因此，當您將scanf的返回值分配給您的變量時，您將覆蓋它已有的正確值。這應該工作：

int rng1; 
scanf("%d", &rng1); 

Answer 3

的scanf()返回的值應始終進行檢查，以確保手術成功。 格式字符串應該（幾乎）總是包含一個前導空格「」 這樣一個遺留的白色空間（如新行）被跳過/消耗 因此，代碼應該更像：

int rng1; 
if(1 != scanf(" %d", &rng1)) 
{ // then, scanf failed 
    perror("scanf for rng1 failed"); 
    exit(EXIT_FAILURE); 
} 

// implied else, scanf for rng1 successful 

Answer 4

AS上面兩個註釋解釋了scnaf（）有返回值只是爲了檢查成功的操作。然而，你需要閱讀的價值是作爲第二個參數。 我也可以看到代碼中的括號不匹配。

int main(int argc, char **argv) 
{ 
    printf("Welcome to my number generator! \n"); 
    printf("What is the first number in the range? \n"); 
    int rng1; 
    int t = scanf("%d", &rng1);     // First scanned value stored in rng1 variable 
    printf("What is the second number in the range? \n"); 
    int rng2; 
    int t1 = scanf("%d", &rng2);     // Second scanned value stored in rng2 variable 
    printf("What would increment would you like to go up in? \n"); 
    int inc; 
    int t2 = scanf("%d", &inc);     // Third scanned value stored in inc variable 

    do 
    { 
     printf("%d\n",rng1); 
     rng1 += inc; 
    } 
    while(rng1 <= rng2);    // repeat until rng1 reaches value of rng2 

    return 0; 
} 

這裏使用臨時變量t，t1和t2，您可以驗證值的掃描是否成功完成。