#include<stdio.h>

#include<stdlib.h>

#include<string.h>

#include<ctype.h>

#define N 200

#define M 20

static int sum=0;/*sum是用来记录目标单词总共出现的次数,必须用static型*/

void checkword(char* p1,char* objectword)
{     

     char temp[M];/*这个数组是用来存取从句子中提取出来的单词*/

     int i=0,j,count=0; 初始值

     while(p1[i]!='\0')
     {

        j=0;

        while(isalpha(p1[i]）)
        {/*用来检测p1[i]是不是字母*/

           temp[j]=p1[i];

           i++;

           j++;

        }

        temp[j]='\0';

        if(strcmp(temp,objectword)==0)/*判断提取出来的单词是否与要查找的单词一致*/

           count++;

        while(!isalpha(p1[i])&&p1[i]!='\0')
        {

           i++;

        }

     }

     if(count!=0)
     {

        sum+=count;

     }         

}

void getsentence(char* p1,FILE* p2,char* objectword)
{

     int i;

     char ch;

     ch=fgetc(p2);  调用fgetc（）函数，括号内为函数的参数，p2为指针

     while(ch!=EOF)  读入的字符不是结束标志
     {

        i=0;

        while(ch!='.'&&ch!=';'&&ch!=EOF)     一直输入字符直到遇到空格或者结束符为止
        {

            p1[i]=ch;

            i++;

            ch=fgetc(p2);

 

        }

        if(ch=='.'||ch==';')
        {

           p1[i]=ch;

           p1[i+1]='\0';   

           checkword(p1,objectword);

           ch=fgetc(p2);

        }

     }

}
                             
int main()
{

    char str1[N],str2[M],filename[M];

    char ch;

    FILE* fp;

    printf("Please input the name of the file:\n");

    scanf("%s",filename);

    printf("Please input the word which you want to search:\n");

    scanf("%s",str2);

    fp=fopen(filename,"r");

    if(fp==NULL)
    {

       printf("cannot open the file\n");

       exit(0);

    }

    getsentence(str1,fp,str2);

    printf("The word which you want to search in the file has been appeared %d times in total!\n",sum);

    fclose(fp);

    system("pause");

    return 0;

}

。

程序本身不复杂，关键是一些库函数怎么用，所以你要查一下文件操作和字符串操作函数的使用方法

你这样问没用，还不如自己网上查查，或看书。。。