C程序设计语言（第二版）3-3

3-3 编写函数expand(s1,s2)，将字符串s1中类似与a-z一类的速记符号在字符串s2中扩展成等价的完整列表abc...xyz。该函数可以处理大小写字母和数字，并可以处理a-b-c、a-z0-9与-a-z等类似的情况

#include<stdio.h>
#include<string.h>

void expand(char* result,char* s2);

int main()
{
    char *s[] = { "a-d-", "a-b-c","z-a-", "-1-6-", 
                  "a-ee-a", "a-R-L", "1-9-1", 
                  "5-5", NULL }; 
    char result[100]=""; 
    int i = 0; 
     
    while ( s[i] ) { 
        expand(result, s[i]); 
      printf("Unexpanded: %s\n", s[i]); 
      printf("Expanded  : %s\n", result); 
                 printf("helloworld\n");
        ++i; 
    }
        return 0;
}

void expand(char * s1, char* s2)
{
        static char upper[27]="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        static char lower[27]="abcdefghigklmnopqrstuvwxyz";
        static char digits[11] = "0123456789"; 

        int i=0;
        int j=0;
        char *start;
        char *end;
        char *p;
        while(s2[i]){
                switch(s2[i]){
                case '-':
                        if(i==0 || s2[i+1]=='\0')
                        {
                                s1[j]='-';
                                j++;
                                i++;
                                break;
                        }
                        else
                        {
                                if( (start = strchr(upper,s2[i-1])) && (end = strchr(upper,s2[i+1])))//如果不存在strchr()返回null
                                        ;
                                else if( (start = strchr(lower,s2[i-1])) && (end = strchr(lower,s2[i+1])))
                                        ;
                                else if( (start = strchr(digits,s2[i-1])) && (end = strchr(digits,s2[i+1])))
                                        ;
                                else{
                                        fprintf(stderr, "EX3_3: Mismatched operands '%c-%c'\n", s2[i-1], s2[i+1]); 
                    s1[j++] = s2[i-1]; 
                    s1[j++] = s2[i++]; 
                    break; 
                                }

                                p=start;
                                while(p!=end){
                                        s1[j]=*p;
                                        if(start<end)
                                                p++;
                                        else
                                                p--;
                                        j++;
                                }
                                s1[j]=*end;
                                j++;
                                s1[j]='-';
                                i=i+2;
                        }
                        break;
                default:
                        if ( s2[i+1] == '-' && s2[i+2] != '\0' ) { 
                ++i; 
            } 
            else {      
                s1[j++] = s2[i++]; 
            } 
            break; 
                }
        }
        s1[j] = s2[i];
        i++;

}

 PS 本例中用到了string.h 中的strchr(str,c)函数，用于查找字符c在字符串str中首次出现的位置的指针，如果找不到，则返回null