C语言基础学习——第1天(类型+操作符)
00main.c
int main(void)
{
return 0;
}
这几行构成了main函数定义的起始部分, 每个C程序都必须有一个main函数, 因为它是程序执行的起点
关键字int表示函数返回一个整形值, 关键字void表示函数不接受任何参数
main函数的函数体包含左花括号和与之相匹配的右花括号之间的任何内容
编译环境: Ubuntu 12.04 gcc version 4.6.3
gcc -c main.c --> 编译单个C源文件, 会产生一个目标文件: main.o
gcc main.o -o main --> 链接这个目标文件, 指定输出的可执行文件名叫做main(不指定的话会默认生成a.out)
gcc main.c --> 这样一步到位也可以得到可执行文件a.out
C语言的编译步骤:
hello.c的编译
1. gcc -E hello.c -o hello.i == gcc -E hello.c > hello.i (得到预处理之后的文件 hello.i)
预处理, 调用预处理器cpp
2. gcc -S hello.c -o hello.s == gcc -S hello.i -o hello.s (得到汇编文件 hello.s)
编译, 调用编译器cc1
3. gcc -c hello.c -o hello.o == gcc -c hello.s -o hello.o (得到目标文件 hello.o)
汇编, 调用汇编器as
4. gcc hello.c -o hello == gcc hello.o -o hello (得到可执行文件 hello)
链接, 调用链接器ld01hello_world.c
#include 02basic_type.c
#include 03literal.c
#include 04scanf.c
#include 05arithmetic_operator.c
#include 06relational_operator.c
#include 07logical_operator.c
#include 08bit_operator.c
#include 09condition_operator.c
#include 10comma_operator.c
#include 11type_cast_1.c
#include 12type_cast_2.c
#include exercise1.c
#include <stdio.h>
int main(void)
{
int i = 0, j = 0;
for(i = 1; i < 10; i++)
{
for(j = 1; j <= i; j++)
{
printf("%dx%d=%02d ", j, i, i*j);
}
printf("\n");
}
printf("\n");
for(i = 9; i > 0; i--)
{
for(j = 1; j <= i; j++)
{
printf("%dx%d=%02d ", j, i, i*j);
}
printf("\n");
}
return 0;
}
练习1: 打印 9 x 9 乘法表
运行结果:
1x1=01
1x2=02 2x2=04
1x3=03 2x3=06 3x3=09
1x4=04 2x4=08 3x4=12 4x4=16
1x5=05 2x5=10 3x5=15 4x5=20 5x5=25
1x6=06 2x6=12 3x6=18 4x6=24 5x6=30 6x6=36
1x7=07 2x7=14 3x7=21 4x7=28 5x7=35 6x7=42 7x7=49
1x8=08 2x8=16 3x8=24 4x8=32 5x8=40 6x8=48 7x8=56 8x8=64
1x9=09 2x9=18 3x9=27 4x9=36 5x9=45 6x9=54 7x9=63 8x9=72 9x9=81
1x9=09 2x9=18 3x9=27 4x9=36 5x9=45 6x9=54 7x9=63 8x9=72 9x9=81
1x8=08 2x8=16 3x8=24 4x8=32 5x8=40 6x8=48 7x8=56 8x8=64
1x7=07 2x7=14 3x7=21 4x7=28 5x7=35 6x7=42 7x7=49
1x6=06 2x6=12 3x6=18 4x6=24 5x6=30 6x6=36
1x5=05 2x5=10 3x5=15 4x5=20 5x5=25
1x4=04 2x4=08 3x4=12 4x4=16
1x3=03 2x3=06 3x3=09
1x2=02 2x2=04
1x1=01exercise2.c
#include
int main(void)
{
int a = 58, b = 87;
int temp = 0;
printf("before: a = %d, b = %d\n", a, b);
temp = a;
a = b;
b = temp;
printf("after: a = %d, b = %d\n", a, b);
printf("\n");
a = 58, b = 87; // 此法可能溢出
printf("before: a = %d, b = %d\n", a, b);
a = a + b;
b = a - b;
a = a - b;
printf("after: a = %d, b = %d\n", a, b);
printf("\n");
a = 58, b = 87;
printf("before: a = %d, b = %d\n", a, b);
a = a ^ b;
b = a ^ b;
a = a ^ b;
printf("after: a = %d, b = %d\n", a, b);
return 0;
}
练习2: 交换整形变量, 方法越多越好
运行结果:
before: a = 58, b = 87
after: a = 87, b = 58
before: a = 58, b = 87
after: a = 87, b = 58
before: a = 58, b = 87
after: a = 87, b = 58 exercise3.c
#include putchar('1') : putchar('0');
if((i != 0) && (i%8 == 0))
putchar('_');
}
putchar('\n');
return 0;
}
练习3: 打印无符号整数的二进制位
运行结果:
input the number: 259
00000000_00000000_00000001_00000011 be careful:
unsigned int i = 0;
for(i = 31; i >= 0; i--)
{
printf("infinite loop\n"); // 无限循环
}
unsigned char j = 0;
for(j = 0; j <= 255; j++)
{
printf("infinite loop\n"); // 同理, 无限循环
}