BSIT Survival Kit

String Functions (<string.h>)

Include <string.h> to use these functions.

Copy

strcpy(destination, source)    // copy source into destination
strncpy(target, source, n)     // copy at most n characters

Concatenation

strcat(str1, str2)             // append str2 to end of str1
strncat(str1, str2, n)         // append at most n characters

Comparison

strcmp(str1, str2)             // returns: <0 if str1<str2, 0 if equal, >0 if str1>str2
stricmp(str1, str2)            // compare, ignoring case
strncmp(str1, str2, n)         // compare at most n characters

Case

strlwr(str)                    // convert to lowercase
strupr(str)                    // convert to uppercase

Length and Other

strlen(str)                    // return length (not counting '\0')
strrev(str)                    // reverse the string in place
strdup(str)                    // return a duplicate
strchr(str, c)                 // pointer to first occurrence of c
strset(str, ch)                // set all characters to ch
strnset(str, ch, n)            // set first n characters to ch

Math Functions (<math.h>) and Character Functions (<ctype.h>)

Mathematical Functions — include `<math.h>`

Function	Syntax	Description
`abs()`	`int abs(int num)`	Absolute value of integer
`fabs()`	`double fabs(double num)`	Absolute value of float
`ceil()`	`double ceil(double num)`	Smallest integer ≥ num (round up)
`floor()`	`double floor(double num)`	Largest integer ≤ num (round down)
`fmod()`	`double fmod(double x, double y)`	Remainder of x/y (float modulus)
`pow()`	`double pow(double base, double exp)`	base raised to exp
`sqrt()`	`double sqrt(double num)`	Square root (num must be ≥ 0)

Character Functions — include `<ctype.h>`

Function	Tests/Does
`isalnum(ch)`	True if letter or digit
`isalpha(ch)`	True if letter
`isdigit(ch)`	True if digit (0–9)
`islower(ch)`	True if lowercase letter
`isupper(ch)`	True if uppercase letter
`ispunct(ch)`	True if punctuation (not space)
`isspace(ch)`	True if whitespace
`tolower(ch)`	Returns lowercase version
`toupper(ch)`	Returns uppercase version

Conversion Functions — include `<stdlib.h>`

Function	Description
`atof(str)`	Convert string to double
`atoi(str)`	Convert string to int
`atol(str)`	Convert string to long int
`itoa(num, str, radix)`	Convert int to string in given base

Practice Exercises — Lesson 7

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Worked Exam Solutions + How-to-Pass Tips — Lesson 7

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Code Lab — Lesson 7: Count the Vowels

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Try It: String, Char & Math

Experiment with other math.h functions like ceil(), floor(), or log(). Try changing the string too.

String Functions (<string.h>)

Copy

Concatenation

Comparison

Case

Length and Other

Math Functions (<math.h>) and Character Functions (<ctype.h>)

Mathematical Functions — include <math.h>

Character Functions — include <ctype.h>

Conversion Functions — include <stdlib.h>

Practice Exercises — Lesson 7

Worked Exam Solutions + How-to-Pass Tips — Lesson 7

Code Lab — Lesson 7: Count the Vowels

Try It: String, Char & Math

Mathematical Functions — include `<math.h>`

Character Functions — include `<ctype.h>`

Conversion Functions — include `<stdlib.h>`