如果 -else if-else 语句没有按预期工作

Question

我在 MacOSX 上使用 'Apple Clang'。

下面的代码是一个移位密码，它使用 8 个不同的移位值之一，具体取决于字符在字符串（即消息）中的位置。

按照规则，它应该编码“ABC”（int 数组 d 设置为 d = {1,2,3,4,5,6,7,8}）并输出 3c 45 45 -6f，而是打印 44 45 46 -6f。 .. 这让我假设 if-else_if-else 语句没有做它们应该做的事情。

[-6f 是终止标记，不依赖于 d[] 或消息。

下面是我尝试的最少的、可重现的例子。

我只包含了缩短的 encrypt() 函数，主函数调用 encrypt() 以及其他函数，分别检查 i 的位置编号 char in msg[] 是 Catalan, Fibonacci , Lucas, Pentagonal, Hexagonal, or Prime number series 的一部分，如果 none 是奇数还是偶数。（有关这些内容的上下文，请查看 here）

#include <stdio>
#include <string.h>
int ctln(int);
int fib(int);
int luc(int);
int pent(int);
int hex(int);
int prm(int);


void encrypt(){
    int d[8]={1,2,3,4,5,6,7,8}
    
    char msg[3002]; int en[3001];
    printf("\nType Message - \n\n"); 
    fgets(msg,sizeof(msg),stdin); // stores message in msg
    int len = strlen(msg); // gets length of string , needs string.h
    if(msg[len-1] == '\n')
         msg[len-1] = '[=10=]'; // to remove \n added by fgets()
    len -- ; // len reduced to position of char before '[=10=]

    char ch; int j;
    for(int i =0;i < len ;i++ ) // for loop en
    {   ch = msg[i];

        if(ctln(i)==1)
            j = ch + d[2];
        else if(fib(i)==1)
            j = ch - d[4];
        else if(luc(i)==1)
            j = ch + d[0];
        else if(pent(i)==1)
            j = ch - d[6];
        else if(hex(i)==1)
            j = ch + d[3];
        else if(prm(i)==1)
            j = ch - d[7];
        else {
            if(i%2 == 0)
                j = ch + d[1];
            else
                j = ch - d[5];
        }
        en[i] = j;
    }
    
    printf("\nEncoded message -\n\n");
    for(int i=0;i < len; i++) // prints hex till last actual char, blocks garbage vals
    {
        printf("%x ", en[i]); // prints shifted char val in hex w.r.t. ASCII 
    }
    printf("-6f\n"); // -6f = -111, used to terminate input in decrypt()
}

int main()
{
    encrypt();
    return 0;
}
int ctln(int x)
{
    int arr[]= {1, 2, 5, 14, 42, 132, 429, 1430};int con=0;
    for(int i =0; i < sizeof(arr); i++){
        if(arr[i] == x)
            con = 1;
    }
    return con;
}

int fib(int x)
{
    int arr[]= {0, 3, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584};
    int con=0;
    for(int i =0; i < sizeof(arr); i++){
        if(arr[i] == x)
            con = 1;
    }
    return con;
}

int luc(int x)
{
    int arr[]= {4, 7, 11, 16, 17, 19, 31, 37, 41, 47, 53, 61, 71, 79, 113, 313, 353, 503, 613, 617, 863, 1097, 1361};
    int con=0;
    for(int i =0; i < sizeof(arr); i++){
        if(arr[i] == x)
            con = 1;
            break;
    }
    return con;
}

int pent(int x)
{
    int arr[]= {12, 22, 35, 51, 70, 92, 117, 145, 176, 210, 247, 287, 330, 376, 425, 477, 532, 590, 651, 715, 782, 852, 925, 1001, 1080, 1162, 1247, 1335, 1426, 1520, 1617, 1717, 1820, 1926, 2035, 2147, 2262, 2380, 2501, 2625, 2752, 2882};
    int con=0;
    for(int i =0; i < sizeof(arr); i++){
        if(arr[i] == x)
            con = 1;
            break;
    }
    return con;
}

int hex(int x)
{
    int arr[]= {0, 1, 6, 15, 28, 45, 66, 91, 120, 153, 190, 231, 276, 325, 378, 435, 496, 561, 630, 703, 780, 861, 946, 1035, 1128, 1225, 1326, 1431, 1540, 1653, 1770, 1891, 2016, 2145, 2278, 2415, 2556, 2701, 2850};
    int con=0;
    for(int i =0; i < sizeof(arr); i++){
        if(arr[i] == x)
            con = 1;
            break;
    }
    return con;
}

int prm(int x)
{
    int arr[]= {7,13,23,29,37,41,43,47,53,59,61,67,71,73,79,83,89,97,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269,271,277,281,283,293,307,311,313,317,331,337,347,349,353,359,367,373,379,383,389,397,401,409,419,421,431,433,439,443,449,457,461,463,467,479,487,491,499,503,509,521,523,541,547,557,563,569,571,577,587,593,599,601,607,613,617,619,631,641,643,647,653,659,661,673,677,683,691,701,709,719,727,733,739,743,751,757,761,769,773,787,797,809,811,821,823,827,829,839,853,857,859,863,877,881,883,887,907,911,919,929,937,941,947,953,967,971,977,983,991,997,1009,1013,1019,1021,1031,1033,1039,1049,1051,1061,1063,1069,1087,1091,1093,1097,1103,1109,1117,1123,1129,1151,1153,1163,1171,1181,1187,1193,1201,1213,1217,1223,1229,1231,1237,1249,1259,1277,1279,1283,1289,1291,1297,1301,1303,1307,1319,1321,1327,1361,1367,1373,1381,1399,1409,1423,1427,1429,1433,1439,1447,1451,1453,1459,1471,1481,1483,1487,1489,1493,1499,1511,1523,1531,1543,1549,1553,1559,1567,1571,1579,1583,1597,1601,1607,1609,1613,1619,1621,1627,1637,1657,1663,1667,1669,1693,1697,1699,1709,1721,1723,1733,1741,1747,1753,1759,1777,1783,1787,1789,1801,1811,1823,1831,1847,1861,1867,1871,1873,1877,1879,1889,1901,1907,1913,1931,1933,1949,1951,1973,1979,1987,1993,1997,1999,2003,2011,2017,2027,2029,2039,2053,2063,2069,2081,2083,2087,2089,2099,2111,2113,2129,2131,2137,2141,2143,2153,2161,2179,2203,2207,2213,2221,2237,2239,2243,2251,2267,2269,2273,2281,2287,2293,2297,2309,2311,2333,2339,2341,2347,2351,2357,2371,2377,2381,2383,2389,2393,2399,2411,2417,2423,2437,2441,2447,2459,2467,2473,2477,2503,2521,2531,2539,2543,2549,2551,2557,2579,2591,2593,2609,2617,2621,2633,2647,2657,2659,2663,2671,2677,2683,2687,2689,2693,2699,2707,2711,2713,2719,2729,2731,2741,2749,2753,2767,2777,2789,2791,2797,2801,2803,2819,2833,2837,2843,2851,2857,2861,2879,2887,2897,2903,2909,2917,2927,2939,2953,2957,2963,2969,2971,2999,3001};
    int con=0;
    for(int i =0; i < sizeof(arr); i++){
        if(arr[i] == x)
            con = 1;
            break;
    }
    return con;
}

主代码中没有编译器errors/warnings，可用here.

Answer 1

感谢 @Martinjames 指出我的 break; 超出了 if 语句的范围，只需使用括号即可修复。

感谢@PaulOgilvie指出

"i < sizeof(arr) 是错误的，因为 sizeof 计算的是字节，而不是整数。使用 i < sizeof(arr)/sizeof(arr[0]) ".
" len-- 仅应在 msg[len-1] == '\n' "

最后，感谢@Someprogrammerdude指点我学习调试，对以后的恐慌很有帮助。

如果 -else if-else 语句没有按预期工作

If -else if- else statement not working as expected

c

arrays

if-statement

function

caesar-cipher