#include <stdio.h>

  int getc(FILE *stream);

#include <stdio.h> //引入标准输入输出库
void main( ) {
  char ch;
  printf ("Input a character: ");  //输入提示信息
  ch = getc(stdin); // 从标准输入控制台中读取字符
  printf ("The character input was: '%c'\n", ch); // 输出字符
}

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
int main(void)
{
  int ch;
  int len;
  int i=0;
  FILE* fstream;
  char msg[100] = "Hello!I have read this file.";
  fstream=fopen("test.txt","at+");
  if(fstream==NULL)
  {
    printf("read file test.txt failed!\n");
    exit(1);
  }
  /*getc从文件流中读取字符*/
  while( (ch = getc(fstream))!=EOF)
  {
    putchar(ch);
  }
  putchar('\n');
  len = strlen(msg);
  while(len>0)/*循环写入*/
  {
    putc(msg[i],fstream);
    putchar(msg[i]);
    len--;
    i++;
  }
  fclose(fstream);
  return 0;
}

#include<stdio.h>

  int ungetc(char c, FILE *stream);

#include<stdio.h>
#include<ctype.h>
int main()
{
  int i=0;
  char ch;
  puts("Input an integer followed by a char:");
  // 读取字符直到遇到结束符或者非数字字符
  while((ch = getchar()) != EOF && isdigit(ch))
  {
    i = 10 * i + ch - 48; // 转为整数
  }
  // 如果不是数字，则放回缓冲区
  if (ch != EOF)
  {
    ungetc(ch,stdin); // 把一个字符退回输入流
  }
  printf("\n\ni = %d, next char in buffer = %c\n", i, getchar());
  system("pause");
  return 0;
}

123ab↙
i *= 123, next char in buffer = a