This document discusses functions in C programming. It defines functions, function prototypes, parameters, return values, and nested function calls. Functions are defined with a return type, name, and parameters. Function prototypes declare the function signature outside of the definition. Parameters are passed by value, so changes inside the function do not affect the original variables. Nested functions call other functions within their implementation.

1. function
• Standard library
• math.h：sqrt
• stdio.h ：printf, scanf

2. Math Library Functions
#include <math.h>
function-name(argument)
printf(“%.2f”, sqrt(900.0));

3. Example: Function
#include <stdio.h>
int square(int);
void main() {
int x;
for (x=1; x<=10; x++)
printf("%d ", square(x));
}
int square(int y) {
return y*y;
} 1 4 9 16 25 36 49 64 81 100

4. Function Definitions
return-value-type function-name(parameter-list)
{
declarations and statements
}
• function-name
• return-value-type
• int
• void
• parameter-list

5. Example: Function Definitions
#include <stdio.h>
int maximum(int, int, int);
void main() {
int a, b, c;
printf("enter three integers: ");
scanf("%d%d%d", &a, &b, &c);
printf("Maximum is: %d", maximum(a, b, c));
}
int maximum(int x, int y, int z) {
int max = x;
if (y>max) max = y;
if (z>max) max = z;
return max;
}
maximum
int int int
int
（interface）

6. Function Prototypes
return-value-type function-name(parameter-list);
• int maximum(int, int, int);

7. Head Files
stdio.h, math.h, string.h
• #include <filename>
• #include <math.h>
• #include “filename”

8. Function Call
main() {
int a, b, c;
scanf("%d%d", &a, &b);
c = max(a, b);
printf("the larger is %d", c);
}
1
2
6
int max(int a, int b) {
int c;
c=a>=b?a:b;
return c;
}
3
4
5

9. Passing Parameters
int max(int a, int b) {
…… return c;
}
main() {
…… c=max(a, b);
}
max()
a
b
c
main()

10. Formal Parameter and Actual Parameter
int max(int a, int b)
{ int c=a>=b?a:b;
return c;
}
main()
{ int a, b, c;
scanf(“%d%d”, &a, &b);
c=max(a, b);
}

11. Formal Parameter
int max(int a, int b)
{ int c=a>=b?a:b;
return c;
}
main()
{ int a, b, c;
scanf(“%d%d”, &a, &b);
c=max(a, b);
}

12. Actual Parameter
int max(int a, int b)
{ int c=a>=b?a:b;
return c;
}
main()
{ int a, b, c;
scanf(“%d%d”, &a, &b);
c=max(a, b);
}

13. Passing Parameters
int max(int a, int b)
{ int c=a>=b?a:b;
return c;
}
main()
{ int x=6, y;
y=max(x, x++);
printf(“%d”, y);
}
b=x++;
a=x;
7

14. Passing Parameters
int max(int a, int b)
{ int c=a>=b?a:b;
a++; b++;
return c;
}
main()
{ int x=6, y=5, z;
z=max(x, y);
printf(“%d,%d,%d”,x,y,z);
}
6,5,6
6
x
5
y
6 a
5 b

15. Passing Parameters
int max(int a, int b)
{ int c=a>=b?a:b;
return c;
}
main()
{ int x=6, y=5, z;
z=max(x, y);
printf(“%d”, z);
}
b=y;
a=x;

16. Returning Results
int max(float a, float b)
{ float c=a>=b?a:b;
return c;
}
main()
{ float x=6.5, y=5.6, z;
z = 2*max(x, y);
printf(“%f”, z);
}
max(x,y)
2*max(x,y)

17. Nested Function Call
• circleArea
• ringArea
r1
r2
circleArea
double
double
ringArea
double double
double
double circleArea(double r);
double ringArea(double r1, double r2);

18. Nested Function Call
#include <stdio.h>
#define PI 3.14
double circleArea(double r);
double ringArea(double r1, double r2);
void main() {
double r1, r2, s;
printf("tInput r1, r2: ");
scanf("%lf%lf", &r1, &r2);
s = ringArea(r1, r2);
printf("ntThe area is:%.2lfn", s);
}

19. Nested Function Call
double circleArea(double r) {
return PI*r*r;
}
double ringArea(double r1, double r2) {
if (r1<=r2)
return circleArea(r2)-circleArea(r1);
else
return circleArea(r1)-circleArea(r2);
}
Input r1, r2: 1 2
The area is: 9.42