函数

前序：
控制台输出结果：

the first experssion is true.

本节课导图：

函数.png

函数的引申：

int main(int argc, const char * argv[]) {
    // insert code here...

    printf("wyy has done as much as iOS as I could fit into 5 days\n");
    printf("Mike has done as much as C as I could fit into 6 days\n");
    printf("Jack has done as much as OC as I could fit into 15 days\n");
    printf("Lisa has done as much as Python as I could fit into 10 days\n");
    printf("Lucy has done as much as Cocoa as I could fit into 7 days\n");

    return 0;
}

可以看到，我们需要输入大量的文字代码，是不是很烦人？其中是否有很多重复性的语句？如果有，我们是否可以提取出来一个函数，来完成这个功能？答案是可以的。

void congratulateStudent (char *student, char *course, int numDays)
{
    printf("%s has done as much as %s as I could fit into %d days\n",student,course,numDays);
}

int main(int argc, const char * argv[]) {
    // insert code here...
    congratulateStudent("wyy", "iOS", 5);
    congratulateStudent("Lucy", "OC", 4);
    congratulateStudent("Jack", "Python", 7);

    return 0;
}

递归调用

void singSong (int num)
{
    if (num == 0) {
        printf("歌曲结束\n");
    }else{
        printf("%d个歌曲\n",num);
        int oneFewer = num - 1;
        singSong(oneFewer);//递归调用
        printf("%d歌曲正在播放\n",num);
    }
}

int main(int argc, const char * argv[]) {
    // insert code here...
    singSong(4);

    return 0;
}

控制台结果:

4个歌曲
3个歌曲
2个歌曲
1个歌曲
歌曲结束
1歌曲正在播放
2歌曲正在播放
3歌曲正在播放
4歌曲正在播放
Program ended with exit code: 0

返回函数值

float triangleArea(float a, float b,float h)
{
    float triangleArea = a * b * h;
    printf("triangleArea is %f.\n",triangleArea);
    return triangleArea;
}

int main(int argc, const char * argv[]) {
    // insert code here...

    triangleArea(2, 3, 4);
    
    return 0;
}

全局变量和静态变量

//float lastTemprature;//全局变量
static float lastTemprature;//静态变量

float fahrenheitFromCelsius(float cel)
{
    lastTemprature = cel;
    float fahr = cel *1.8+32.0;
    printf("%f Celsius is %f Fahrenheit\n",cel,fahr);

    return fahr;
}

int main(int argc, const char * argv[]) {
    // insert code here...

    float freezeInC = 0;
    float freezeInF = fahrenheitFromCelsius(freezeInC);
    printf("the lastTemprature %f \n",freezeInF);

    return EXIT_SUCCESS;
}

练习题：
已知三角形内角和一定是180度，试创建一个新项目，类型为基于C语言的command Line Tool名称为 Triangle。在main.c编写一个函数，参数是某两个内角的角度，返回值一个剩下的第三个内角的角度。

答案见下一章，写对者红包奖励哦。欢迎初学者多多参与。