#include<stdio.h>
int main()
{
char string[100];
int i,num=0,word=0;
char c;
gets(string);                                                          //输入一个字符串给字符数组string
for(i=0;(c=string[i])!='\0';i++)                                       //只要字符不是'\0'就继续执行循环
  if(c==' ')word=0;                                                    //如果是空格字符，使word=0
  else if(word==0)                                                     //如果不是空格字符且word原值为0
 {                              
   word=1;                                                             //使word=1
   num++;                                                              //num累加1，表示增加一个单词
}
printf("There are %d words in this line.\n",num);                      //输出单词数
return 0;
}

利用指针做吧！

#include"stdio.h"
void main()
{
    char str[100],c;
    int i=0,j=0;
    gets(str);
    c=str[i];
    for(i=0;(c=str[i])!='\0';i++)
    {
        if((c=str[i])>'A' && (c=str[i])<'z')
            j++;
    }
    printf("%d\n",j);

}