for循环的使用

1. 1-100的和

        let sum = 0
        for (let i = 1; i <= 100; i++) {
            sum += i
        } console.log(sum);

2. 三行五列的星星

        let star = ''
        for (let i = 1; i <= 3; i++) {
            for (let j = 1; j <= 5; j++) {
                star += '*'
            }
            star += '\n'
        }
        console.log(star);

3. 正三角形

        let sjx = ''
        for (let i = 1; i <= 9; i++) {
            for (let j = 1; j <= i-1; j++) {
                sjx += '^'
            }
            sjx += '\n'
        }
        console.log(sjx);

4. 倒三角形

        let sjx = ''
        for (let i = 1; i <= 9; i++) {
            for (let j = i; j <= 9; j++) {
                sjx += '^'
            }
            sjx += '\n'
        }
        console.log(sjx);

5. 九九乘法表

        let sum = ''
        for (let i = 1; i <= 9; i++) {
            for (let j = 1; j <= i; j++) {
                sum += j + '*' + i + '=' + (i * j) + '\t'
            }
            sum += '\n'
        }
        console.log(sum);