C语言查找一个字符串中指定字符的个数

#include <stdio.h>
int find_char (char **strings,char value)
{
    int num=0;
    char *string;
    while((string= *strings++)!=NULL)
    {
        while(*string!='')
        {
            if(*string++==value)
            {
             num++;
            }
        }
    }
    return num;
}

void main( )
{
 char *str[100] = { "aaabccdaaa" };
 int s_num;
 s_num=find_char(str,'a');
 printf("s_num=%d
",s_num);    
 system("PAUSE"); 
}