The "1" in the string() function call indicates the number of times the second parameter, which is a character, is repeated. In the example provided, string(1, '0' + i % 10) creates a string consisting of a single character derived from the expression '0' + i % 10. The string constructor in C++ can take two parameters: the first is the count of repetitions, and the second is the character to be repeated. For instance, string(1, 'H') results in "H", while string(2, 'H') results in "HH". Additionally, the string constructor can also be called with a single character parameter, such as string('H'), which similarly returns "H". The function is part of the <string> library in C++.