未定义的对“WinMain”的引用

Question

我在CodeBlocks中运行以下C编写代码时遇到问题：

#include <stdio.h>
#include <stdlib.h>


#define STRLEN 5

int readln(char s[], int maxlen) {
    char ch;
    int i;
    int chars_remain;
    i = 0;
    chars_remain = 1;
    while (chars_remain) {
        ch = getchar();
        if ((ch == '\n') || (ch == EOF)) {
            chars_remain = 0;
        } else if (i < maxlen - 1) {
            s[i] = ch;
            i++;
        }
    }
    s[i] = '\0';
    return i;
}

int main(int argc, char **argv) {
    char firstname[STRLEN];
    char lastname[STRLEN];
    int len_firstname;
    int len_lastname;
    printf("Enter your first name:");
    len_firstname = readln(firstname, STRLEN);
    printf("Enter your last name:");
    len_lastname = readln(lastname, STRLEN);
    printf("Hello, %s, %s\n", firstname, lastname);
    printf("Length of firstname = %d, lastname = %d", len_firstname, len_lastname);
}

这是错误消息：

未定义引用`WinMain @ 16＆＃39; 错误：ld返回1退出状态

所以我是新手，但我认为它与我的编译器有关。任何有关如何解决它的线索非常感谢！