專案1：

#include <stdio.h>
int main()
{
    char c;
    int i;
    scanf("%d",&i);
    while((c=getchar())!='\n')
    {
        putchar(c-i);
    }
    return 0;
}

專案2：迴圈加密

//迴圈加密
#include <stdio.h>
int main()
{
    char c;
    while((c=getchar())!='\n')
    {
        if((c>='W' && c<='Z') || (c>='w' && c<='z'))
            putchar(c-22);
        else
            putchar(c+4);
    }
    return 0;
}
 

#include <stdio.h>
int main()
{
    char c,frontIsSpace=0;
    while((c=gerchar())!='\n')
    {
        if(c!=' ')
        {
            frontIsSpace=0;
            putchar(c);
        }
        else if(frontIsSpace==0)
        {
            putchar(c);
            frontIsSpace=1;
        }
    }
    return 0;
}
 

#include <stdio.h>
int main()
{
    char blood;
    int a=0,b=0,o=0,ab=0;
    printf("請輸入血型序列(A,B,O,C(C代表AB型)):");
    while((blood=getchar())!='X')
    {
        switch(blood)
        {
            case 'A':
                a++;break;
            case 'B':
                b++;break;
            case 'O':
                o++;break;
            case 'C':
                ab++;break;
        }
    }
    printf("A:%d\t",a);
    printf("B:%d\t",b);
    printf("O:%d\t",o);
    printf("AB:%d\n",ab);
    return 0;
}
 

#include <stdio.h>
int main()
{
    char c;
    int n=0,s=0,l=0,total=0;
    printf("Please enter a sentence:");
    scanf("%c",&c);
    while(c!='\n')
    {
        if(c>='0' && c<='9')
            n++;
        else if(c==' ')
            s++;
        else if((c>='a'&&c<='z')||(c>='A'&&c<='Z'))
            l++;
        total++;
        scanf("%c",&c);
    }
    printf("Number:%d\n",n);
    printf("Space:%d\n",s);
    printf("Letter:%d\n",l);
    printf("Character:%d\n",total);
    return 0;
}