C语言笔记

初始化动态二维矩阵

#include<stdio.h>
#include<stdlib.h>
int** matrix(int height,int width,int initial)
{
    int **a=malloc(sizeof *a * height);
    printf("Initializing matrix of size %d X %d with initial value %d\n", height,width,initial);
    for(int i=0;i<height;i++)
    {
        a[i]=malloc(sizeof *(a[i]) * width);
        for(int j=0;j<width;j++)
        {
            a[i][j]=initial;
        }
    }
    printf("Printing the matrix...\n");
    for(int i=0;i<height;i++)
    {
        for(int j=0;j<width;j++)
        {
            printf("%d ",a[i][j]);
        }
        printf("\n");
    }
}
int main(void)
{
    int** m=matrix(4,5,0);
    return 0;
}

分析复杂变量声明

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

#define MAXTOKEN 100

enum { NAME, PARENS, BRACKETS};

void dcl(void);
void dirdcl(void);

int gettoken(void);
int tokentype;
char token[MAXTOKEN];
char name[MAXTOKEN];
char datatype[MAXTOKEN];
char out[1000];

main()
{
    while (gettoken() != EOF) {
        strcpy(datatype, token);
        out[0] = '\0';
        dcl();
        if (tokentype != '\n')
            printf("syntax error\n");
        printf("%s: %s %s\n", name, out, datatype);
    }
    return 0;
}

/* dcl: parse a declarator */
void dcl(void)
{
    int ns;
    for (ns = 0; gettoken() == '*'; ) /* count *'s */
        ns++;
    dirdcl();
    while (ns-- > 0)
        strcat(out, " pointer to");
}

/* dirdcl: parse a direct declarator */
void dirdcl(void)
{
    int type;
    if (tokentype == '(') { /* ( dcl ) */
        dcl();
        if (tokentype != ')')
            printf("error: missing )\n");
    } else if (tokentype == NAME) /* variable name */
        strcpy(name, token);
    else
        printf("error: expected name or (dcl)\n");
    while ((type=gettoken()) == PARENS || type == BRACKETS)
        if (type == PARENS)
           strcat(out, " function returning");
        else {
            strcat(out, " array");
            strcat(out, token);
            strcat(out, " of");
        }
}


int gettoken(void)
{
    int c, getch(void);
    void ungetch(int);
    char *p = token;

    while ((c = getch()) == ' ' || c == '\t')
        ;
    if (c == '(') {
        if ((c = getch()) == ')') {
            strcpy(token, "()");
            return tokentype = PARENS;
        } else {
            ungetch(c);
            return tokentype = '(';
        }
    } else if (c == '[') {
        for (*p++ = c; (*p++ = getch()) != ']'; )
            ;
        *p = '\0';
        return tokentype = BRACKETS;
    } else if (isalpha(c)) {
        for (*p++ = c; isalnum(c = getch()); )
            *p++ = c;
        *p = '\0';
        ungetch(c);
        return tokentype = NAME;
    } else
        return tokentype = c;
}

#define BUFSIZE 100

char buf[BUFSIZE];
int bufp = 0;

int getch(void)
{
    return (bufp >0) ? buf[--bufp] : getchar();
}

void ungetch(int c)
{
    if (bufp >= BUFSIZE)
        printf("üngetch: too many characters\n");
    else
        buf[bufp++] = c;
}

打印进度条

void progress_bar(const int n, const int tot)
{
    int i, pgr = n*50/tot, rem = (tot-n)*50/tot;
    printf("\r[");
    for (i=0; i<pgr; i++)
        printf("#");
    for (i=0; i<rem; i++)
        printf("-");
    printf("]");
}

lambda表达式

#define lambda(lambda$_ret, lambda$_args, lambda$_body)\
  // 语句表达式
  ({\
    lambda$_ret lambda$__anon$ lambda$_args\
      lambda$_body\
    lambda$__anon$;\ // 返回值
  })

注释切换代码

#include<stdio.h>
int main(){
/**
  printf("1\n");
/*/
  printf("2\n");
//*/

/**/
  printf("3\n");
/*/
  printf("4\n");
//*/
    return 0;
}