c语言之条件编译

#include<stdio.h>
#include<iostream>
#define CORRECT "myfirst"


int main() {
    char str[10];
    int func(char* str1, char* str2);
    printf("输出你最喜欢的：n");
    scanf("%s", str);

//如果没有定义CORRECT宏名，则在接下来进行定义
#ifndef CORRECT
#define CORRECT "test"
#endif // CORRECT
    if (func(str, CORRECT) == 0) {
        printf("谢谢你n");
    }
    else
    {
        printf("不好意思了n");
    }
    system("pause");
    return 0;
}
int func(char* str1, char* str2) {
    return strcmp(str1, str2);
}

#include<stdio.h>
#include<iostream>
#define ROUND 1
#define PI 3.14

int main() {
    int a,b;
    double c;
    a = 2;
    b = 3;
//如果ROUND为1，那么运行接下来的语句
#if ROUND
    c = (a + b)*PI*2;
    printf("%.2fn", c);
//否则运行下面的语句
#else
    c = a + b;
#endif
    system("pause");
    return 0;
}