C语言编程练习

1、一个数组中只有两个数字是出现一次，其他所有数字都出现了两次。
找出这两个数字，编程实现。

#include<stdio.h>
#include<stdlib.h>
#include<assert.h>
void sort(int* arr, int sz) {
assert(arr!=NULL);
 for (int i = 0; i < sz - 1; i++) {
  for (int j = 0; j < sz - 1-i; j++) {
   if (arr[j] > arr[j + 1]) {
    int tmp = arr[j + 1];
    arr[j + 1] = arr[j];
    arr[j] = tmp;
   }
  }
 }
}
void Tofind_num(int* arr, int sz,int* num1,int* num2) {
assert(arr!=NULL);
assert(num1!=NULL);
assert(num2!=NULL);
 int tmp = 0;
 for (int i = 0; i < sz; i+=2) {
  if (arr[i] == arr[i + 1]) {
   continue;
  }
  else{
   if (tmp == 0) {
    *num1 = arr[i];
    ++i;
   }
   else if(tmp == 1){
    *num2 = arr[i];
    ++i;
   }
   ++tmp;
  }
 }
}
int main() {
 int arr[10] = { 2,1,3,5,6,5,4,2,4,3 };
 int sz = sizeof(arr) / sizeof(arr[0]);
 int num1, num2;
 sort(arr, sz);
 Tofind_num(arr, sz,&num1,&num2);
 printf("%d %d\n",num1,num2);
 system("pause");
 return 0;
}

2、喝汽水，一瓶汽水1元，两个空瓶可以换一瓶汽水，给20元，可以喝多少汽水 ，编程实现。

int main() {
 int total_bottle = 20;
 int empty_bottle = 20;
 int surplus_empty_bottle = 0;
 while (empty_bottle >= 1) {
  empty_bottle = empty_bottle + surplus_empty_bottle;
  total_bottle = total_bottle + empty_bottle / 2;
  surplus_empty_bottle = empty_bottle % 2;
  empty_bottle = empty_bottle / 2;
 }
 printf("total_bottle = %d瓶\n", total_bottle);
 system("pause");
 return 0;
}

3、模拟实现strcpy，strcat，strcmp，strlen

size_t Strlen(const char* arr) {
 assert(arr != NULL);
 size_t a = 0;
 while (*arr != '\0') {
  arr++;
  ++a;
 }
 return a;
}
char* Strcat(char* arr, const char* brr) {
 assert(arr != NULL);
 assert(brr != NULL);
 int i = 0;
 for (; arr[i] != '\0'; ++i);
 for (int j = 0; brr[j] != '\0'; ++j,++i) {
  arr[i] = brr[j];
 }
 arr[i] = '\0';
 return arr;
}
char* Strcpy(char* dest, const char* src) {
 assert(dest != NULL);
 assert(src != NULL);
 int i = 0;
 for (; dest[i] != '\0'; ++i) {
  dest[i] = src[i];
 }
 return dest;
}
int Strcmp(const char* arr, const char* brr) {
 assert(arr != NULL);
 assert(brr != NULL);
 int i = 0;
 for (; arr[i] != '\0'&&brr[i] != '\0'; ++i) {
  if (arr[i] < brr[i]) {
   return -1;
  }
  else if (arr[i] > brr[i]) {
   return 1;
  }
  else  {
  
  }
 }
 if (arr[i] < brr[i]) {
  return -1;
 }
 else if (arr[i] > brr[i]) {
  return 1;
 }
 else {
  return 0;
 }
}
int main() {
 char arr[20] = "abc";
 char brr[10] = "def";
 printf("%d\n",Strlen(arr));
 Strcat(arr, brr);
 printf("%s\n", arr);
 Strcpy(arr, brr);
 printf("%s\n", arr);
 int ret = Strcmp(arr, brr);
 if (ret == 0) {
  printf("arr == brr\n");
 }
 else if (ret < 0) {
  printf("arr < brr\n");
 }
 else if (ret > 0) {
  printf("arr >brr\n");
 }
 system("pause");
 return 0;
}