Question

#include <stdio.h>

int main()
{
    char _char = 32;
    int x, p, i, d;
    scanf("%d ", &x);
    while(_char == 32)
        _char = getchar();
    x = x%26;
    printf("The encrypted string is: ");
    while((_char >= 'a' && _char <= 'z') || (_char >= 'A' && _char <= 'Z'))
    {
        if(_char >= 'a' && _char <= 'z')
            _char = 'a' + (_char + x - 'a')%26;
        else
            _char = 'A' + (_char + x - 'A')%26;
        d = 'a' - 'A';
        p = (_char >= 'a') ? _char - d : _char + d;
        printf("%c", p);
        scanf("%c", &_char);
    }
    return 0;
}

Code description : the program receives a number ‘x’ followed by spaces and then a sequence of letters , then it will print these letters (modified) until the first number or when there is no more letters to receive . It works fine when I run it in Code blocks but when I use CMD to insert the inputs as a file , this gives me an infinite loop if I insert :

1   FffF 

when I add 0 or any number it works fine :

1   FffF0

the infinite loop is sth like :

The encrypted string is:
BBBcccDDDeeefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz....

how can I slove this !?

Answer 1

If there is no more input to scan,

 scanf("%c", &_char);

doesn’t modify _char. You have to check the return value of the scan,

if (scanf("%c",&_char) < 1) break;

to exit the loop then.