1.關系表達式和邏輯表達式
單目運算符 ! 邏輯非
算術運算符 加 減 乘 除 取模
關系運算符 > < >= <= == !=
邏輯運算符 && ||
上述運算符優先級從上至下依次遞減
選擇結構程式設計
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
int main()
{
int i;
while (scanf("%d", &i) != EOF)
{
if (i > 0) {//在if括号後面不能加;
printf("i is bigger than 0.\n");
}else if(i == 0){
printf("i is equal to 0.\n");
}else {
printf("i is smaller than 0.\n");
}
}
}
循環結構程式設計
while語句:
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
//從1加到100
int main()
{
int i = 1;
int total = 0;
while (i <= 100) {
total = total + i;
i++;
}
printf("total = %d", total);
}
for語句:
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
// 從1加到100
int main()
{
int i, total;
//for語句括号内隻能兩個分号
for (i = 1, total = 0; i <= 100; i++)
{
total = total + i;
}
printf("total = %d\n", total);
}
continue語句:
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
//求1-100之間的奇數總和
int main()
{
int i, total;
for (i = 1, total = 0; i <= 100; i++)
{
if (i % 2 != 0) {
continue; // 跳出本次循環
}
total = total + i;
}
printf("total = %d\n", total);
}
break語句:
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
int main()
{
int i, total;
for (i = 1, total = 0; i <= 100; i++)
{
if (total > 2000) {
break;//當求和大于2000,就終止循環
}
total = total + i;
}
printf("total = %d, i = %d\n", total, i);
}
練習:
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
/*
輸入一個整型數,判斷是否為對稱數,如果是,輸出yes,否則輸出no
例如:12321是對稱數,輸出yes,124421是對稱數,輸出yes,1231不是
對稱數,輸出no
*/
int main()
{
//思路:把最初輸入的整型數a,反過來存入另一
// 個整型數b,然後判斷是否與原數相等
// 相等就是yes,否則no
int a, b, temp;
while (scanf("%d", &a) != EOF) {
temp = a;
b = 0;
while (a) {
b = b * 10 + a % 10;
a = a / 10;
}
a = temp;
printf("a = %d, b = %d\n", a, b);
if (a == b) {
printf("yes\n");
}
else {
printf("no\n");
}
}
return 0;
}