如何循环字符串中的每个字母？

#include <stdio.h>

int main()

#include <stdio.h>

int main()

{
    char msg[31] = {'\0'};
    char encrypted[31] = {'\0'};
    int key;


    printf("Please enter a message under 30 characters: ");
    fgets(msg, 31, stdin);

    printf("Please enter an encryption key: ");
    scanf("%d", &key);

    int i = 0;

    while (msg[i] && ('a' <= msg[i] <= 'z' || 'A' < msg[i] < 'Z'))
{
    encrypted[i] = (msg[i] + key);
    i++;
}

    printf("%s\n", msg);
    printf("%d\n", key);
    printf("%s\n", encrypted);

}

Okay i've got my code to increment the characters but i don't know how to make it ignore special characters and spaces. Also how do i use % to loop back to 'a' and 'A'?

好的,我有我的代码来增加字符,但我不知道如何使它忽略特殊字符和空格。另外我如何使用%循环回'a'和'A'?

Thank you.

3 个解决方案

#1

You just need a simple for loop:

你只需要一个简单的for循环:
```
for (int i = 0; i < 31; i++)
{
    // operate on msg[i]
}
```
If you didn't know the length of the string to begin with, you might prefer a while loop that detects the null terminator:

如果你不知道字符串的长度,你可能更喜欢检测空终止符的while循环:
```
int i = 0;
while (msg[i])
{
    // operate on msg[i]
    i++;
}
```
Your fgets and scanf are probably fine, but personally, I would be consistent when reading input, and fgets for it all. Then you can sscanf to get key out later.

你的fgets和scanf可能很好,但就个人而言,我会在阅读输入时保持一致,并为此付出一切代价。然后你可以sscanf稍后获取密钥。

#2

scanf and fgets seem fine in this situation the way you've used them.

scanf和fgets在这种情况下看起来很好用你使用它们的方式。

In C, a string is just an array of characters. So, you access each element using a for loop and array indexing:

在C中,字符串只是一个字符数组。因此,您使用for循环和数组索引访问每个元素:

for (int i = 0; i < strlen(str); i++) {
  char thisChar = str[i];
  //Do the processing for each character
}

You can perform arithmetic on thisChar as necessary, but be careful not to exceed 255. You might want to put a check on key to ensure it doesn't get too big.

您可以根据需要对thisChar执行算术运算,但请注意不要超过255.您可能需要检查密钥以确保它不会变得太大。

#3

Getting a string from scanf:

从scanf获取字符串:

char msg[31];
scanf("%30s", msg);

OR (less efficient, because you have to fill the array with 0s first)

或者(效率较低,因为你必须首先用0填充数组)

char msg[31] = { 0 };
scanf("%30c", msg);

Iterating a string is as easy a for loop (be sure to use c99 or c11)

迭代字符串就像循环一样简单(一定要使用c99或c11)

int len = strlen(msg);
for(int i = 0; i < len; i++) {
    char current = msg[i];
    //do something
    msg[i] = current;
}

"Encrypting" (i.e. ciphering) a character require a few steps

“加密”(即加密)一个角色需要几个步骤

Determine if we have an uppercase character, lowercase character, or non-alphabetic character

确定我们是否有大写字符,小写字符或非字母字符

Determine the position in the alphabet, if alphabetic.

如果是字母,则确定字母表中的位置。

Update the position, using the modulus operator (%)

使用模数运算符更新位置(%)

Correct the position, if alphabetic

如果是字母,请更正位置

I could give you the code here, but then you wouldn't learn anything from doing it yourself. Instead, I encourage you to implement the cipher based on the steps I provided above.

我可以在这里给你代码,但是你不会自己学习任何东西。相反,我鼓励您根据我上面提供的步骤实现密码。

Note that you can do things like:

请注意,您可以执行以下操作:

char c = 'C';
char e = 'E' + 2; 
char lower_c = 'C' - 'A' + 'a';

#1

You just need a simple for loop:

你只需要一个简单的for循环:
```
for (int i = 0; i < 31; i++)
{
    // operate on msg[i]
}
```
If you didn't know the length of the string to begin with, you might prefer a while loop that detects the null terminator:

如果你不知道字符串的长度,你可能更喜欢检测空终止符的while循环:
```
int i = 0;
while (msg[i])
{
    // operate on msg[i]
    i++;
}
```
Your fgets and scanf are probably fine, but personally, I would be consistent when reading input, and fgets for it all. Then you can sscanf to get key out later.

你的fgets和scanf可能很好,但就个人而言,我会在阅读输入时保持一致,并为此付出一切代价。然后你可以sscanf稍后获取密钥。

#2