C programming – Loop until user inputs number scanf

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scanf returns the count of items that it has successfully read according to your format. You can set up a loop that exits only when scanf("%d", &number2); returns 1. The trick, however, is to ignore invalid data when scanf returns zero, so the code would look like this:

while (scanf("%d",&number2) != 1) {
    // Tell the user that the entry was invalid
    printf("You did not enter a valid number\n");
    // Asterisk * tells scanf to read and ignore the value
    scanf("%*s");
}

Since you read a number more than once in your code, consider making a function to hide this loop, and call this function twice in your main to avoid duplication.

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