Why functions segments of code that repeat several times better readability abstraction of code smaller program size IAG0581

Structural programming int main(void){ int a, b, c; do{ printf("Please enter A: "); scanf("%d", &a); if(a <= 0) printf("A must be positive!\n"); }while(a <= 0); printf("Please enter B: "): scanf("%d", &b); if(b <= 0) printf("B must be positive!\n"); }while(b <= 0); //... return 0; } IAG0581

Functional programming int readPositiveInt(char *name){ int x; do{ printf("Please enter %s: ", name); scanf("%d", &x); if(x <= 0) printf("%s must be positive!\n", name); }while(x <= 0); return x; } int main(void){ int a, b, c; a = readPositiveInt("A"); b = readPositiveInt("B"); //... return 0; IAG0581

Declaring a function returntype functionName(parameters){ functionBody } parameters is just a list of variables separated by comma: int a, int b use "void" if no parameters IAG0581

Datatypes, simple types char a single character or small number: int integer number float floating point number void signifies no type When used as parameters, these are unidirectional IAG0581

Datatypes, pointers char * pointer to a character or character array int * pointer to integer or integer array float * pointer to float or floating point array void * pointer to memory without type specified When used as parameters, these are bidirectional IAG0581

Datatypes, arrays char[] a character array int[] an array of integers float[] a array of floating point numbers When used as parameters, these are bidirectional IAG0581

Calling a function even if no parameters, ( ) are necessary even if function returns something it can be called without assignment For example: int doSmth(void){ //... return 1; } int main(void){ doSmth(); return 0; IAG0581

C compiler single pass compiler accepts only variables and functions that have been declared before they are used sometimes necessary to declare that a function exists before providing code for that function IAG0581

Function prototypes used to tell compiler that a function by that name exists and what parameter types it takes parameter names are unimportant For example: int readPositiveInt(char *); IAG0581

Function prototypes int readPositiveInt(char *); int main(void){ //... a = readPositiveInt("A"); } int readPositiveInt(char *name){ IAG0581

Variable scope variable exists in block where it is declared outside block it doesn't exist variable can be redefined in an inner block each function is separate block IAG0581

Variable scope int fn1(void){ int x = 2; //... } int main(void){ int a, b, x; x = 5; a = fn1(); if(a < b){ float x = 3.0; x++; IAG0581

Function with no data exchange void welcome(void){ printf("This program ..."); printf("Written by..."); } int main(void){ welcome(); ... IAG0581

Getting a result from a function result is returned with return keyword. what's returned should be of same type as declared returntype, if not it will be converted IAG0581

Getting a result from a function int test(void){ float f = 0.8; return f; // will return 0, cos converted to int } int test2(void){ ... return; //warning !! void test3(void){ int x = 10; return x; //warning !! IAG0581

Getting multiple results only 1 item of returntype can be returned returntype could be complex type, like record or pointer etc. use pointers as parameters so function can access memory outside of its scope Example you should know: scanf("%d", &a); & operator returns address of where variable is located in memory IAG0581

Getting multiple results int div(int a, int b, int *result, int *remainder){ if(b == 0) return 0; *result = a / b; *remainder = a % b; return 1; } int main(void){ //... int s, t; div(15, 6, &s, &t); IAG0581

Getting multiple results with arrays arrays are always pointers to first element function can access all elements if it knows how many there are IAG0581

Getting multiple results with arrays void doSmth(int n, float M[n]){ int i; for(i = 0; i < n; i++) M[i] = //... } int main(void){ int Arr[10]; doSmth(10, Arr); ... IAG0581

Conditions a function call can be put anywhere in code, also in place of conditions if you have complex condition then make it into a function, especially if needed more than once For example: while( a < b && a < c || a + b < c + 1 ){ //... } IAG0581

Conditions int isTrue(int a, int b, int c){ return a < b && a < c || a + b < c + 1; } int main(void){ //... if(!isTrue(3, b, x)) while(isTrue(3, b, x)){ IAG0581

Function as parameter permits you call a function that has been passed as a parameter to your code alternatively you can write a function that behaves as a parameter for some function you want to call typical example qsort void qsort (void* base, size_t num, size_t size, int (*compar)(const void*,const void*)); IAG0581

Function qsort() qsort() sorts an array if you supply it a function that can compare 2 elements in it, essentially a condition function int isLess(const void *aa, const void *bb){ int *a = (int*)aa; int *b = (int*)bb; return (*a) - (*b); } int main(void){ int M[10]; //... qsort(M, 10, sizeof(int), isLess); IAG0581

Function as parameter int readInt(char *name, int (*suits)(int), char *cond){ int x; do{ printf("Please enter %s: ", name); scanf("%d", &x); if(!suits(x)) printf("%s must be %s!\n", name, cond); }while(!suits(x)); return x; } int isPos(int a){ return a > 0; int main(void){ int a, b, c; a = readInt("A", isPos, "positive"); b = readInt("B", isPos, "positive"); //... IAG0581