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function calls - call by value and call by name
Pointers and references example from a Well House Consultants training course
More on Pointers and references [link]
Source code: fourth.c Module: C207
#include <stdio.h>
/* This example shows two functions which do something similar, except that one is call by value (so the incoming variable's value is copied in and doesn't alter the one in the caling code), and the other is called by name (so that the incoming variable's value IS changed within the calling code when we alter it in the function */ int triple(int incoming) { int outgoing; outgoing = incoming * 3; incoming = incoming - 4; return outgoing; } int quadrle(int * incoming) { int outgoing; outgoing = *incoming * 4; *incoming = *incoming - 5; return outgoing; } main() { int stuff = 14; int thing = 17; int lots; int oodles; lots = triple(stuff); /* Tries but fails to alter stuff */ printf("You have %d\n",lots); printf("You sent %d\n",stuff); /* Original value */ oodles = quadrle(&thing); /* Pass ADDRESS in */ printf("You have %d\n",oodles); printf("You sent %d\n",thing); /* changed by function */ } /* Sample output munchkin:capr grahamellis$ ./fourth You have 42 You sent 14 <<< YES! since triple just altered its own copy You have 68 You sent 12 <<< NO! altering within quadre munchkin:capr grahamellis$ */ Learn about this subject
This module and example are covered on the following public courses:
* Learning to Program in C * Learning to program in C and C++ * Programming in C * C and C++ Programming * Learning to program in C and C++ * C and C++ Programming Also available on on site courses for larger groups Books covering this topic
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