for循环
1.1、for循环语法
for (expression1; condition; expression2) {statement...}
1.2、示例
sum = 0; for (i = 0; i <= 100; i++) {sum += i} printf("sum = %d, i = %d\n", sum, i)
sum = 0;
for (i = 0; i <= 100; i++) {
    sum += i
}
printf("sum = %d, i = %d\n", sum, i)