次 cì

For measuring the times of repeated actions

去一次 qù yí cì / qù yi cì

做一次 zuò yí cì / zuò yi cì

试一次 shì yí cì / shì yi cì

如果可以的话，一周去一次。 Rúguǒ kěyǐ de huà, yì zhōu qù yí cì.
'Go once a week if you can.'

你通常只需这样做一次。 Nǐ tōngcháng zhǐ xū zhèyàng zuò yí cì.
'You usually only have to do this once.'

如果你想要的话，我们可以再试一次。 Rúguǒ nǐ xiǎngyào de huà, wǒmen kěyǐ zài shì yi cì.
'We can have another try if you want.'

N.B.

When the number of repeated actions is one, there are two ways to pronounce 一. If you need to emphasize the number, 一 should have a tone. If you need to emphasize the action, 一 should be neutral.

Used when describing a story which happened in the past

有一次 yǒu yí cì

她从来没被抓过，不过有一次，警报响了。 Tā cónglái méi bèi zhuāguo, búguò yǒu yí cì, jǐngbào xiǎng le.
'She never got caught but, once, the alarm went off.'