7-11---14

/* 进制转换 */
#include<stdio.h>
int main(void)
{
    int  i,k;
    char str1[80],str2[80];
    long number;

    printf("Enter a string:");
    i=0;
    while((str1[i]=getchar())!='\n')
        i++;
    str1[i]='\0';



    k=0;
    for(i=0;str1[i]!='\0';i++)
        if 
    (str1[i]>='0'&&str1[i]<='9'||str1[i]>='a'&&str1[i]<='f'||str1[i]>='A'&&str1[i]<='F')
        {
            str2[k]=str1[i];
            k++;
        }
    str2[k]-'\0';


    number=0;
    for(i=0;str2[i]!='\0';i++)
        if(str2[i]>='0'&&str2[i]<='9')
            number=number*16+str2[i]-'0';
        else if(str2[i]>='a'&&str2[i]<='f')
            number=number*16+str2[i]-'a'+10;
        else if(str2[i]>='A'&&str2[i]<='F')
            number=number*16+str2[i]-'A'+10;


    printf("New string:");
    for(i=0;str2[i]!='\0';i++)
        putchar(str2[i]);
    printf("\n");
    printf("number=%1d\n",number);


    return 0;
}

/* 统计字符串中数字字符的个数 */
#include<stdio.h>
int main(void)
{
    int count,i;
    char str[80];



    printf("Enter a string:");
    i=0;
    while((str[i]=getchar())!='\n')
        i++;
    str[i]='\0';


    count=0;
    for(i=0;str[i]!='\0';i++)
        if(str[i]<='9'&&str[i]>='0')
            count++;
    printf("count=%d\n",count);



    return 0;
}

/* 判断字符串是否是回文 */
#include<stdio.h>
int main(void)
{
    int i,n,m;
    char s[10];



    printf("Enter a string:");
    i=0;
    while((s[i]=getchar())!='\n')
        i++;
    s[i]='\0';


    for(n=0,m=i-1;n<m;n++,m--)
        if(s[n]!=s[m])
            break;
    if(n>=m)
        printf("It is a plalindrome\n");
    else 
        printf("It is not a plalindrome\n");


    return 0;
}

#include<stdio.h>
int main(void)
{
    int i,number;
    char str[10];



    printf("Enter a string:");
    i=0;
    while((str[i]=getchar())!='\n')
        i++;
    str[i]='\0';



    number=0;
    for(i=0;str[i]!='\0';i++)
        if(str[i]>='0'&&  str[i]<='9')
            number=number*10+str[i]-'0';



    printf("digit=%d\n",number);



    return 0;
}