我要怎么判断这个“.”

创建一个名为count的函数，用来判断用户输入的字符串中“.”（句号）的个数并返回

int count(char *p){
    char *s = p;
    int cnt = 0;
    while(*s != '\0'){
        if(*s == '.'){
            cnt ++;
        }
        s ++;
    }
    return cnt;
}

遍历字符串比较每个字符是否为 .，计数就行了

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

int count(char t[])
{
    int j,c=0;
    int n=strlen(t);
    for(j=0; j<n; j++)
    {
        if(t[j]=='.')
        {
            c++;
        }
    }
    return c;
}
int main()
{
    char t[250];
    printf("输入字符串：");
    gets(t);
    printf("'.'的个数为：%d",count(t));

    return 0;
}

#include <stdio.h>

#define N 256

int count(const char *s)
{
    int n = 0;
    while (*s)
        if (*s++ == '.')
            n++;
    return n;
}

int main()
{
    char a[N];
    fgets(a, N, stdin);
    printf("%d", count(a));
    return 0;
}

#include<stdio.h>
int count(char str[])
{
    int i=0;
    int res=0;
    while (str[i] != '\0') {
        if (str[i]=='.')
        {
            res++;
        }
        i++;
    }
    return res;
}
int main()
{
    char str[1024] = {0};
    gets_s(str);
    
    int c = count(str);
    printf("%d\n", c);
    return 0;
}