Arithmetic

1
2
3
4
5
6
7

#include <stdio.h>
int main(){
    int a = 1, b = 2, sum = 0;
    sum = a + b;
    printf("%d", sum);
    return 0;
}

• 變數
  • 每個變數都必須有它的型別
  • 在使用變數前必須先宣告它
• 在C裡面， = 意思為”指定”，而不是”相等”，指派右邊的數值給左邊的變數
• 一個好習慣，總是初始化變數
• C Spec:
  • C89:If an object that has static storage duration is not initialized explicitly, it is initialized implicitly.
  • C99: If it has arithmetic type, it is initialized to (positive or unsigned) zero.

• In C99: a == (a / b) * b + a % b
• printf 是一個函式去印出格式化字串
  • %d -> 有號十進位整數
  • %f -> 十進位浮點數
  • %u -> 無號十進位整數
  • 當然不只這些
• 小技巧

1
2
3
4
5

a += b -> a = a + b
a -= b -> a = a - b
a *= b -> a = a * b
a /= b -> a = a / b
a %= b -> a = a % b

• 查看記憶體使用大小： sizeof()，回傳單位為 byte ( printf("%lu", sizeof()); )
• #include <stdint.h>
  • int8_t: 8-bit signed interger
  • int16_t: 16-bit signed interger
  • int32_t: 32-bit signed interger
  • int64_t: 64-bit signed interger
  • uint8_t: 8-bit unsigned interger
  • uint16_t: 16-bit unsigned interger
  • uint32_t: 32-bit unsigned interger
  • uint64_t: 64-bit unsigned interger

• 輸入：scanf("%d", &a);
  • 至於為甚麼需要 &，之後會在指標的章節介紹到
  • scanf 是否有回傳值? ( man 3 scanf )

• 最後也最重要的技能：RTFM and STFG