C语言基础语法学习笔记——流程控制

NS图、流程图

分类

顺序：语句逐句执行 选择：出现了一种以上的情况 循环：在某个条件成立的情况下，重复执行某个动作

关键字

选择：if-else switch-case 循环：while do-while for if-goto 辅助控制：continue break

1、选择语句if-else

格式：

if (exp)
    cmd;

if (exp)
    cmd1;
else
    cmd2;

注意：else只与最近的if匹配，与缩进无关

#include 

int main(void)
{
    int a = 1, b = 1, c = 2;

    if (a == b)
        if (b == c)
            printf("a == b == c\n");
    else
        printf("a != b\n");  // a != b

    if (a == b)
    {
        if (b == c)
            printf("a == b == c\n");
    }
    else
        printf("a != b\n");

    return 0;
}

#include 

int main(void)
{
    int score, res;

    while (1)
    {
        printf("Enter a score[0,100]: ");
        res = scanf("%d", &score);

        if (res <= 0) break;

        if (score < 0 || score > 100)
        {
            fprintf(stderr, "Bad input\n");
            break;
        }

        if (score >=90 && score <= 100)
            puts("A");
        else if (score >=80 && score < 90)
                puts("B");
              else if (score >= 70 && score < 80)
                        puts("C");
                    else if (score >= 60 && score < 70)
                            puts("D");
                         else if (score >= 0 && score < 60)
                                puts("E");
    }

    return 0;
}

2、选择语句switch-case

格式：

switch (exp)
{
    case 常量或常量表达式:
        break;
    case 常量或常量表达式:
        break;
    deault:
        ;
}

#include 

int main(void)
{
    int score, res;

    while (1)
    {
        printf("Please enter a score: ");
        res = scanf("%d", &score);

        if (res <= 0) break;

        if (score < 0 || score > 100)
        {
            fprintf(stderr, "EINVAL\n");
            break;
        }

        switch (score / 10)
        {
            case 10:
            case 9:
                puts("A");
                break;
            case 8:
                puts("B");
                break;
            case 7:
                puts("C");
                break;
            case 6:
                puts("D");
                break;
            case 5:
            case 4:
            case 3:
            case 2:
            case 1:
            case 0:
                puts("E");
                break;
            default:
                fprintf(stderr, "Unknown\n");
                break;
        }
    }

    return 0;
}

#include 

int main(void)
{
    int ch;
    ch = getchar();

    switch (ch)
    {
        case 'a':
        case 'A':
            puts("Ant: a very small insect that lives under the ground in large and well-organized social groups.");
            break;
        case 'b':
        case 'B':
            puts("Butterfly: a type of insect with large, often brightly coloured wings");
            break;
        case 'c':
        case 'C':
            puts("Cobra: a poisonous snake from Africa and southern Asia that makes itself look bigger and more threatening by spreading the skin at the back of its head");
            break;
        case 'd':
        case 'D':
            puts("Donkey: an animal like a small horse with long ears");
            break;
        default:
            fprintf(stderr, "EINVAL\n");
            break;
    }

    return 0;
}