React Native - How to access variable between two buttons - react-native

Question

Trying to learn react native here and want to reuse a variable between two "buttons" to perform tasks.
Take for example a simple workflow:
When the user presses Start a random number is generated and a
message is displayed
When the user presses Check I do some checking and display a
message according to the results.
This is my approach:
state = {
statusText: "Press Start to begin",
randNum: 0,
};
generateRandNum = () => {
var rand = Math.floor(Math.random() * 100);
return rand;
};
pressStart = () => {
this.setState({
randNum: this.generateRandNum(),
statusText: "started; " + randNum, //display randnum for simple check-debug
});
};
pressCheck = () => {
this.setState({
statusText: "checked; ",
});
};
Above, when pressStart is pressed, returns an error saying randNum is not found.
This, however, does work, but now can't access the variable elsewhere
pressStart = () => {
this.setState({
statusText: "started; " + this.generateRandNum(), //display randnum for simple check-debug
});
};
How can I properly update randNum to the generated number so that I can access it globally?
==== While the answer below works this is what I ended up using, which seems to work just the same.
pressCheck = () => {
this.setState({
statusText: "checked; " + this.state.randNum,
});
};

Answer 1

You never initialize randNum anywhere, so in order to use it in both places, you should give it a value before the setState.
Try this :
pressStart = () => {
const randNum = this.generateRandNum()
this.setState({
randNum: randNum,
statusText: "started; " + randNum, //display randnum for simple check-debug
});
};
pressCheck = () => {
this.setState(oldState => ({
...oldState,
statusText: "checked; " + oldState.randNum,
}));
};