用c语言循环统计子字符串substr在字符串str中出现的次数

可以使用两层循环遍历字符串str，逐个匹配判断是否为子字符串substr，并在匹配成功时计数器加1。具体代码如下：

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

int count_substr(const char* str, const char* substr) {
    int count = 0;
    int len_str = strlen(str);
    int len_substr = strlen(substr);
    for (int i = 0; i < len_str - len_substr + 1; i++) {  // 遍历字符串str
        int j;
        for (j = 0; j < len_substr; j++) {  // 遍历子字符串substr
            if (str[i+j] != substr[j])
                break;
        }
        if (j == len_substr)  // 匹配成功
            count++;
    }
    return count;
}

int main() {
    char str[] = "hello world, hello everyone!";
    char substr[] = "hello";
    int count = count_substr(str, substr);
    printf("'%s' appears %d times in '%s'\n", substr, count, str);
    return 0;
}

输出：

'hello' appears 2 times in 'hello world, hello everyone!'