20131007国庆作业例7-11,7-12，7-13,7-14

7-11

结果1

结果2

#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; 
} 

7-12

#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; 
} 

7-13

#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; 
} 

7-14

#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;
}