please tell me a proper defination of a function?

[sana.pari]

Aslam-u-alaikum!

Sir,

please tell me a proper defination of a function?

[Support]

Dear Student,
Most useful programs are much larger than the programs that we have considered so far. To make large programs manageable, programmers modularize them into subprograms. Functions (called methods or procedures in other programming languages) allow the programmer to modularize a program by separating its tasks into self-contained units. There are several motivations for modularizing a program with functions. One is the divide-and-conquer approach, which makes program development more manageable by making programs from small, simple pieces. The statements in the function bodies are written only once, and can be reused from several locations in a program.